This is where it is crashing:

$ gdb --args python3 /usr/bin/update-manager --no-update 

... snip ...

Thread 1 "python3" received signal SIGSEGV, Segmentation fault.
Downloading source file /usr/src/glib2.0-2.80.0-6ubuntu3.1/debian/build/deb/../../../gobject/gtype.c
0x00007ffff7137d59 in g_type_check_instance_is_fundamentally_a (                
    type_instance=0x39383131204c2035, fundamental_type=0x50)
    at ../../../gobject/gtype.c:4151
warning: 4151	../../../gobject/gtype.c: No such file or directory
(gdb) p type_instance
$1 = 0x39383131204c2035
(gdb) p *type_instance
Cannot access memory at address 0x39383131204c2035
(gdb) where
#0  0x00007ffff7137d59 in g_type_check_instance_is_fundamentally_a
    (type_instance=0x39383131204c2035, fundamental_type=0x50)
    at ../../../gobject/gtype.c:4151
#1  0x00007ffff711c959 in g_object_ref (_object=0x39383131204c2035)
    at ../../../gobject/gobject.c:4199
#2  0x00007ffff61123c6 in gdk_event_copy (event=0x2803cf0)
    at ../../../gdk/gdkevents.c:661
#3  0x00007ffff72e1c4f in pygi_boxed_copy_in_place (self=0x7fffea0a5a30)
    at ../gi/pygi-boxed.c:223
#4  arg_boxed_to_py_cleanup
    (state=<optimized out>, arg_cache=<optimized out>, cleanup_data=0x7fffea0a5a30, data=<optimized out>, was_processed=<optimized out>)
    at ../gi/pygi-struct-marshal.c:527
#5  0x00007ffff72d63e6 in pygi_marshal_cleanup_args_to_py_marshal_success
    (state=state@entry=0x7fffffffc110, cache=<optimized out>)
    at ../gi/pygi-marshal-cleanup.c:156
#6  0x00007ffff72d680a in _pygi_closure_handle
    (cif=<optimized out>, result=<optimized out>, args=<optimized out>, data=<optimized out>) at ../gi/pygi-closure.c:589
#7  0x00007ffff7fad641 in ffi_closure_unix64_inner
    (cif=<optimized out>, fun=<optimized out>, user_data=<optimized out>, rvalue=<optimized out>, reg_args=<optimized out>, argp=0x7fffffffc3c0 "\020\304\377\377\377\177") at ../src/x86/ffi64.c:899
--Type <RET> for more, q to quit, c to continue without paging--
#8  0x00007ffff7fadd38 in ffi_closure_unix64 () at ../src/x86/unix64.S:303
#9  0x00007ffff5934d5d in _gtk_tree_view_column_cell_event
    (flags=0, cell_area=0x7fffffffc440, event=0x2803cf0, tree_column=0x260ed10 [GtkTreeViewColumn]) at ../../../gtk/gtktreeviewcolumn.c:2930
#10 gtk_tree_view_multipress_gesture_pressed
    (gesture=0x25b7a20 [GtkGestureMultiPress], n_press=1, x=<optimized out>, y=<optimized out>, tree_view=<optimized out>) at ../../../gtk/gtktreeview.c:3356

#15 0x00007ffff7130883 in <emit signal 'pressed' on instance 0x25b7a20 [GtkGestureMultiPress]>
    (instance=instance@entry=0x25b7a20, signal_id=<optimized out>, detail=detail@entry=0) at ../../../gobject/gsignal.c:3583
    #11 0x00007ffff5699b43 in _gtk_marshal_VOID__INT_DOUBLE_DOUBLEv
    (closure=<optimized out>, return_value=<optimized out>, instance=<optimized out>, args=<optimized out>, marshal_data=<optimized out>, n_params=<optimized out>, param_types=0x164d240) at gtk/gtkmarshalers.c:4804
    #12 0x00007ffff71306bd in _g_closure_invoke_va
    (param_types=0x164d240, n_params=<optimized out>, args=0x7fffffffc720, instance=0x25b7a20, return_value=0x0, closure=0x25b7d90)
    at ../../../gobject/gclosure.c:897
    #13 signal_emit_valist_unlocked
    (instance=instance@entry=0x25b7a20, signal_id=signal_id@entry=344, detail=detail@entry=0, var_args=var_args@entry=0x7fffffffc720)
    at ../../../gobject/gsignal.c:3424
--Type <RET> for more, q to quit, c to continue without paging--
    #14 0x00007ffff71307c1 in g_signal_emit_valist
    (instance=0x25b7a20, signal_id=344, detail=0, var_args=var_args@entry=0x7fffffffc720) at ../../../gobject/gsignal.c:3263
#16 0x00007ffff57b603e in gtk_gesture_multi_press_begin
    (gesture=0x25b7a20 [GtkGestureMultiPress], sequence=sequence@entry=0x0)
    at ../../../gtk/gtkgesturemultipress.c:242
#21 0x00007ffff7130883 in <emit signal 'begin' on instance 0x25b7a20 [GtkGestureMultiPress]>
    (instance=instance@entry=0x25b7a20, signal_id=<optimized out>, detail=detail@entry=0) at ../../../gobject/gsignal.c:3583
    #17 0x00007ffff71148da in g_cclosure_marshal_VOID__BOXEDv
    (closure=0xf5c7e0, return_value=<optimized out>, instance=0x25b7a20, args=<optimized out>, marshal_data=<optimized out>, n_params=<optimized out>, param_types=0xf61450) at ../../../gobject/gmarshal.c:1686
    #18 0x00007ffff71306bd in _g_closure_invoke_va
    (param_types=0xf61450, n_params=<optimized out>, args=0x7fffffffcb10, instance=0x25b7a20, return_value=0x0, closure=0xf5c7e0)
    at ../../../gobject/gclosure.c:897
    #19 signal_emit_valist_unlocked
    (instance=instance@entry=0x25b7a20, signal_id=signal_id@entry=339, detail=detail@entry=0, var_args=var_args@entry=0x7fffffffcb10)
    at ../../../gobject/gsignal.c:3424
    #20 0x00007ffff71307c1 in g_signal_emit_valist
--Type <RET> for more, q to quit, c to continue without paging--
    (instance=0x25b7a20, signal_id=339, detail=0, var_args=var_args@entry=0x7fffffffcb10) at ../../../gobject/gsignal.c:3263
#22 0x00007ffff57adfd6 in _gtk_gesture_set_recognized
    (recognized=<optimized out>, sequence=0x0, gesture=0x25b7a20 [GtkGestureMultiPress]) at ../../../gtk/gtkgesture.c:344
#23 _gtk_gesture_set_recognized
    (sequence=0x0, recognized=1, gesture=0x25b7a20 [GtkGestureMultiPress])
    at ../../../gtk/gtkgesture.c:330
#24 _gtk_gesture_check_recognized
    (gesture=gesture@entry=0x25b7a20 [GtkGestureMultiPress], sequence=sequence@entry=0x0) at ../../../gtk/gtkgesture.c:390
#25 0x00007ffff57b5c9c in gtk_gesture_handle_event
    (controller=0x25b7a20 [GtkGestureMultiPress], event=<optimized out>)
    at ../../../gtk/gtkgesture.c:757
#26 0x00007ffff57b95ca in gtk_gesture_single_handle_event
    (controller=0x25b7a20 [GtkGestureMultiPress], event=0x279f6e0)
    at ../../../gtk/gtkgesturesingle.c:222
#27 0x00007ffff5778ab3 in gtk_event_controller_handle_event
    (controller=0x25b7a20 [GtkGestureMultiPress], event=0x279f6e0)
    at ../../../gtk/gtkeventcontroller.c:230
#28 0x00007ffff595e658 in _gtk_widget_run_controllers
    (widget=0x25c39c0 [GtkTreeView], event=0x279f6e0, phase=GTK_PHASE_BUBBLE)
    at ../../../gtk/gtkwidget.c:7447
--Type <RET> for more, q to quit, c to continue without paging--
#29 0x00007ffff569d0a4 in _gtk_marshal_BOOLEAN__BOXED
    (closure=0xec96d0, return_value=0x7fffffffced0, param_values=0x7fffffffcf60, marshal_data=<optimized out>, invocation_hint=<optimized out>, n_param_values=<optimized out>)
    at gtk/gtkmarshalers.c:84
#30 0x00007ffff71102fa in g_closure_invoke (closure=0xec96d0, return_value=0x7fffffffced0, n_param_values=2, param_values=0x7fffffffcf60, invocation_hint=0x7fffffffceb0)
    at ../../../gobject/gclosure.c:834
#31 0x00007ffff713ff98 in signal_emit_unlocked_R.isra.0
    (node=node@entry=0x7fffffffd050, detail=detail@entry=0, instance=instance@entry=0x25c39c0, emission_return=emission_return@entry=0x7fffffffd0d0, instance_and_params=instance_and_params@entry=0x7fffffffcf60) at ../../../gobject/gsignal.c:3928
#32 0x00007ffff712fef2 in signal_emit_valist_unlocked (instance=instance@entry=0x25c39c0, signal_id=signal_id@entry=85, detail=detail@entry=0, var_args=var_args@entry=0x7fffffffd1c0)
    at ../../../gobject/gsignal.c:3533
#33 0x00007ffff71307c1 in g_signal_emit_valist (instance=0x25c39c0, signal_id=85, detail=0, var_args=var_args@entry=0x7fffffffd1c0) at ../../../gobject/gsignal.c:3263
#34 0x00007ffff7130883 in g_signal_emit (instance=instance@entry=0x25c39c0, signal_id=<optimized out>, detail=detail@entry=0) at ../../../gobject/gsignal.c:3583
#35 0x00007ffff5966b74 in gtk_widget_event_internal.part.0.lto_priv.0 (widget=0x25c39c0 [GtkTreeView], event=0x279f6e0) at ../../../gtk/gtkwidget.c:7812
#36 0x00007ffff5803310 in propagate_event_up (topmost=<optimized out>, event=<optimized out>, widget=0x25c39c0 [GtkTreeView]) at ../../../gtk/gtkmain.c:2598
#37 propagate_event (widget=widget@entry=0x25c39c0 [GtkTreeView], event=event@entry=0x279f6e0, captured=captured@entry=0, topmost=topmost@entry=0x0) at ../../../gtk/gtkmain.c:2701
#38 0x00007ffff580343f in gtk_propagate_event (event=0x279f6e0, widget=0x25c39c0 [GtkTreeView]) at ../../../gtk/gtkmain.c:2735
#39 0x00007ffff5803eaa in gtk_main_do_event (event=0x279f6e0) at ../../../gtk/gtkmain.c:1921
#40 gtk_main_do_event (event=<optimized out>) at ../../../gtk/gtkmain.c:1691
#41 0x00007ffff6108407 in _gdk_event_emit (event=0x279f6e0) at ../../../gdk/gdkevents.c:73
#42 _gdk_event_emit (event=0x279f6e0) at ../../../gdk/gdkevents.c:67
#43 0x00007ffff6161c6e in gdk_event_source_dispatch.lto_priv () at ../../../gdk/x11/gdkeventsource.c:354
#44 0x00007ffff71bb5b5 in g_main_dispatch (context=0xe13030) at ../../../glib/gmain.c:3344
#45 0x00007ffff721a717 in g_main_context_dispatch_unlocked (context=0xe13030) at ../../../glib/gmain.c:4152
#46 g_main_context_iterate_unlocked.isra.0 (context=0xe13030, block=block@entry=1, dispatch=dispatch@entry=1, self=<optimized out>) at ../../../glib/gmain.c:4217
#47 0x00007ffff71bbf77 in g_main_loop_run (loop=0x2c1dd10) at ../../../glib/gmain.c:4419
#48 0x00007ffff57feb45 in gtk_main () at ../../../gtk/gtkmain.c:1329
#49 0x00007ffff7fadb16 in ffi_call_unix64 () at ../src/x86/unix64.S:104
#50 0x00007ffff7faa3ef in ffi_call_int (cif=cif@entry=0x26b3798, fn=<optimized out>, rvalue=<optimized out>, avalue=<optimized out>, closure=closure@entry=0x0) at ../src/x86/ffi64.c:673
#51 0x00007ffff7fad0be in ffi_call (cif=cif@entry=0x26b3798, fn=<optimized out>, rvalue=rvalue@entry=0x7fffffffd768, avalue=<optimized out>) at ../src/x86/ffi64.c:710
#52 0x00007ffff72d7bcb in pygi_invoke_c_callable (function_cache=0x26b36f0, state=<optimized out>, py_args=<optimized out>, py_kwargs=<optimized out>) at ../gi/pygi-invoke.c:684
#53 0x00007ffff72d611a in pygi_function_cache_invoke (py_kwargs=0x7fffea0908c0, py_args=0xb476a8 <_PyRuntime+76264>, function_cache=<optimized out>) at ../gi/pygi-cache.c:862
#54 pygi_callable_info_invoke (user_data=0x0, cache=<optimized out>, kwargs=0x7fffea0908c0, py_args=0xb476a8 <_PyRuntime+76264>, info=<optimized out>) at ../gi/pygi-invoke.c:727
#55 _wrap_g_callable_info_invoke (self=<optimized out>, py_args=0xb476a8 <_PyRuntime+76264>, kwargs=0x7fffea0908c0) at ../gi/pygi-invoke.c:764
#56 0x000000000054b0dc in PyObject_Call () at ../Objects/call.c:376
#57 0x00000000005db593 in _PyEval_EvalFrameDefault (tstate=tstate@entry=0xba5048 <_PyRuntime+459656>, frame=<optimized out>, frame@entry=0x7ffff7fb2020, throwflag=throwflag@entry=0)
    at Python/bytecodes.c:3254
#58 0x00000000005d59ab in _PyEval_EvalFrame (throwflag=0, frame=0x7ffff7fb2020, tstate=0xba5048 <_PyRuntime+459656>) at ../Include/internal/pycore_ceval.h:89
#59 _PyEval_Vector (kwnames=0x0, argcount=0, args=0x0, locals=0x7ffff75f9e40, func=0x7ffff75da200, tstate=0xba5048 <_PyRuntime+459656>) at ../Python/ceval.c:1683
#60 PyEval_EvalCode (co=co@entry=0xc42ca0, globals=globals@entry=0x7ffff75f9e40, locals=locals@entry=0x7ffff75f9e40) at ../Python/ceval.c:578
#61 0x0000000000608ac2 in run_eval_code_obj (locals=0x7ffff75f9e40, globals=0x7ffff75f9e40, co=0xc42ca0, tstate=0xba5048 <_PyRuntime+459656>) at ../Python/pythonrun.c:1722
#62 run_mod (mod=<optimized out>, filename=<optimized out>, globals=0x7ffff75f9e40, locals=0x7ffff75f9e40, flags=<optimized out>, arena=<optimized out>) at ../Python/pythonrun.c:1743
#63 0x00000000006b4d83 in pyrun_file
    (fp=fp@entry=0xbf53e0, filename=filename@entry=0x7ffff75f9ff0, start=start@entry=257, globals=globals@entry=0x7ffff75f9e40, locals=locals@entry=0x7ffff75f9e40, closeit=closeit@entry=1, flags=0x7fffffffdc48) at ../Python/pythonrun.c:1643
#64 0x00000000006b4aea in _PyRun_SimpleFileObject (fp=fp@entry=0xbf53e0, filename=filename@entry=0x7ffff75f9ff0, closeit=closeit@entry=1, flags=flags@entry=0x7fffffffdc48)
    at ../Python/pythonrun.c:433
#65 0x00000000006b491f in _PyRun_AnyFileObject (fp=0xbf53e0, filename=filename@entry=0x7ffff75f9ff0, closeit=closeit@entry=1, flags=flags@entry=0x7fffffffdc48) at ../Python/pythonrun.c:78
--Type <RET> for more, q to quit, c to continue without paging--
#66 0x00000000006bc9c5 in pymain_run_file_obj (skip_source_first_line=0, filename=0x7ffff75f9ff0, program_name=0x7ffff75f9fb0) at ../Modules/main.c:360
#67 pymain_run_file (config=0xb47c28 <_PyRuntime+77672>) at ../Modules/main.c:379
#68 pymain_run_python (exitcode=0x7fffffffdc3c) at ../Modules/main.c:629
#69 Py_RunMain () at ../Modules/main.c:709
#70 0x00000000006bc4ad in Py_BytesMain (argc=<optimized out>, argv=<optimized out>) at ../Modules/main.c:763
#71 0x00007ffff7c2a1ca in __libc_start_call_main (main=main@entry=0x518a50 <main>, argc=argc@entry=3, argv=argv@entry=0x7fffffffde88) at ../sysdeps/nptl/libc_start_call_main.h:58
#72 0x00007ffff7c2a28b in __libc_start_main_impl
    (main=0x518a50 <main>, argc=3, argv=0x7fffffffde88, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffde78) at ../csu/libc-start.c:360
#73 0x0000000000657925 in _start ()