apt install anything fails due to grub error

[Karl Stenerud]

Ubuntu 20.04 desktop, running on a Ryzen 5 laptop.

$ sudo apt install vlc
[sudo] password for karl:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  bridge-utils linux-modules-5.4.0-29-generic python3-attr python3-cached-property python3-docker python3-dockerpty python3-docopt
  python3-importlib-metadata python3-jsonschema python3-more-itertools python3-pyrsistent python3-texttable python3-websocket python3-zipp
  ubuntu-fan
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  libaribb24-0 libbasicusageenvironment1 libcddb2 libdca0 libdvbpsi10 libebml4v5 libfaad2 libgroupsock8 libixml10 libkate1 liblivemedia77
  libmatroska6v5 libmpcdec6 libopenmpt-modplug1 libplacebo7 libprotobuf-lite17 libproxy-tools libqt5x11extras5 libresid-builder0c2a
  libsdl-image1.2 libsdl1.2debian libsidplay2 libspatialaudio0 libsrt1 libssh2-1 libupnp13 libusageenvironment3 libvlc-bin libvlc5
  libvlccore9 libxcb-xv0 vlc-bin vlc-data vlc-l10n vlc-plugin-base vlc-plugin-notify vlc-plugin-qt vlc-plugin-samba vlc-plugin-skins2
  vlc-plugin-video-output vlc-plugin-video-splitter vlc-plugin-visualization
Suggested packages:
  libdvdcss2
The following packages will be REMOVED:
  linux-image-5.4.0-29-generic
The following NEW packages will be installed:
  libaribb24-0 libbasicusageenvironment1 libcddb2 libdca0 libdvbpsi10 libebml4v5 libfaad2 libgroupsock8 libixml10 libkate1 liblivemedia77
  libmatroska6v5 libmpcdec6 libopenmpt-modplug1 libplacebo7 libprotobuf-lite17 libproxy-tools libqt5x11extras5 libresid-builder0c2a
  libsdl-image1.2 libsdl1.2debian libsidplay2 libspatialaudio0 libsrt1 libssh2-1 libupnp13 libusageenvironment3 libvlc-bin libvlc5
  libvlccore9 libxcb-xv0 vlc vlc-bin vlc-data vlc-l10n vlc-plugin-base vlc-plugin-notify vlc-plugin-qt vlc-plugin-samba vlc-plugin-skins2
  vlc-plugin-video-output vlc-plugin-video-splitter vlc-plugin-visualization
0 upgraded, 43 newly installed, 1 to remove and 10 not upgraded.
2 not fully installed or removed.
Need to get 0 B/13,8 MB of archives.
After this operation, 60,5 MB of additional disk space will be used.
Do you want to continue? [Y/n]
INFO Requesting to save current system state
Successfully saved as "autozsys_86qdrr"
Extracting templates from packages: 100%
(Reading database ... 301000 files and directories currently installed.)
Removing linux-image-5.4.0-29-generic (5.4.0-29.33) ...
/etc/kernel/postrm.d/initramfs-tools:
update-initramfs: Deleting /boot/initrd.img-5.4.0-29-generic
/etc/kernel/postrm.d/zz-update-grub:
/usr/sbin/grub-probe: error: failed to get canonical path of `rpool/ROOT/ubuntu_kofpnr'.
run-parts: /etc/kernel/postrm.d/zz-update-grub exited with return code 1
dpkg: error processing package linux-image-5.4.0-29-generic (--remove):
 installed linux-image-5.4.0-29-generic package post-removal script subprocess returned error exit status 1
dpkg: too many errors, stopping
Errors were encountered while processing:
 linux-image-5.4.0-29-generic
Processing was halted because there were too many errors.
INFO Updating GRUB menu
ERROR "update-grub" returned an error: exit status 1
E: Sub-process /usr/bin/dpkg returned an error code (1)

I'm not sure why apt keeps calling grub, but something in grub is broken. I've never messed with grub in any way, nor has this machine been used for anything other than basic web browsing and software development.