This is not a virtual machine. I have a PPA for "mkusb" but no errors reported on mkusb. There has been an error for "bcmwl-kernel-source" for awhile but I don't need wifi on this machine.
The only "non-stock" issue is I have both "devel" & "groovy" in the apt sources list, trying to get my ubuntu install to be somewhat "rolling" and possibly that pulls in conflicting packages??
I booted back into MATE and into a TTY and ran your list of commands . . . I don't know how to copy/paste from the TTY, so back in the GUI I again ran your "grep" and "aptitude" commands. Looks like there are residuals left over from when I had ticked the "pre-release" box recently, and that brought in "5.8 kernel & packages" that had a similar "crashing of GUI effect" . . . .
$ grep -ir ^deb /etc/apt --include=*.list
/etc/apt/sources.list.d/mkusb-ubuntu-unstable-groovy.list:deb Index of /mkusb/unstable/ubuntu groovy main
/etc/apt/sources.list:deb Index of /ubuntu devel main restricted
/etc/apt/sources.list:deb Index of /ubuntu devel-updates main restricted
/etc/apt/sources.list:deb Index of /ubuntu devel universe
/etc/apt/sources.list:deb Index of /ubuntu devel-updates universe
/etc/apt/sources.list:deb Index of /ubuntu devel multiverse
/etc/apt/sources.list:deb Index of /ubuntu devel-updates multiverse
/etc/apt/sources.list:deb Index of /ubuntu devel-security main restricted
/etc/apt/sources.list:deb Index of /ubuntu devel-security universe
/etc/apt/sources.list:deb Index of /ubuntu devel-security multiverse
/etc/apt/sources.list:deb Index of /ubuntu groovy universe main
:~$ sudo aptitude search "~o"
[sudo] password:
idA libcdio18 - library to read and control CD-ROM
i A libprocps7 - library for accessing process information
i A linux-5.4-headers-5.4.0-14 - Header files related to Linux kernel versi
i A linux-headers-5.4.0-14-generic - Linux kernel headers for version 5.4.0 on
i A linux-headers-5.4.0-9 - Header files related to Linux kernel versi
i linux-headers-5.4.0-9-generic - Linux kernel headers for version 5.4.0 on
i A linux-headers-5.8.0-12 - Header files related to Linux kernel versi
i A linux-headers-5.8.0-12-generic - Linux kernel headers for version 5.8.0 on
i linux-image-5.4.0-9-generic - Signed kernel image generic
i A linux-modules-5.4.0-9-generic - Linux kernel extra modules for version 5.4