(a) GTK being used in the gnome-shell process (usually by extensions); and
(b) The absence of an Xserver for GTK to connect to (Xwayland is only started on-demand now).
It looks like one possible offender using GTK is gnome-shell-extension-appindicator. I'm not sure about the other extensions, and it's hard to tell with desktop-icons-ng which in theory uses GTK in a safe way (in a separate client process).
Like the similar upstream bug https:/ /gitlab. gnome.org/ GNOME/mutter/ -/issues/ 1475, this appears to be caused by the intersection of:
(a) GTK being used in the gnome-shell process (usually by extensions); and
(b) The absence of an Xserver for GTK to connect to (Xwayland is only started on-demand now).
It looks like one possible offender using GTK is gnome-shell- extension- appindicator. I'm not sure about the other extensions, and it's hard to tell with desktop-icons-ng which in theory uses GTK in a safe way (in a separate client process).