Such a strange thing has just happened to my laptop, which had been running Fedora 33 64-bit (KDE spin). It went a little something like this:
I saw in the system tray a Software Updates notification that packages were ready to install (it checks once a day which I think is how it came configured by default). I scrolled through the list as I usually do to get an idea of what would be upgraded, then clicked the button to get the upgrade under way, noticed that the download was a little under 200MB, and then put it out of my mind and got back to what I had been doing.
Some time later, my machine crashed. It started with all open windows, window decorations, and panels disappearing bar two or three windows. Ctrl+alt+Fx took me to blank windows with no login prompts. Ctrl+alt+delete did nothing either in those windows or in the X server.
I’m a bit hazy on the details of what happened next. I know that I powered off the machine and then powered back on again, but I can’t remember whether I managed to boot to desktop (followed by another crash as above) once more prior to that which followed, but in any case, that which followed was that on boot (I use UEFI), my hard disk was not recognised, and I could only boot from a Fedora 32 Live USB stick which I thankfully had at hand.
I managed to restore the missing UEFI boot by following the excellent instructions by Franz Nemeth here: https://fnemeth.net/posts/2019/02/fixing-a-missing-or-broken-uefi-record-on-fedora-29/
Oddly, though, I noticed while doing that that /etc/fedora-release had reverted from release 33 to release 32. When I managed to boot up into my system again, it appeared that, indeed, my applications (most if not all of them) had reverted to their 32 versions - including the Linux kernels in /boot, the highest version of which had reverted to 5.7.12-200.
Has anybody else experienced this sort of weirdness? I am in the middle of the process of updating all packages and then performing (for the second time) the upgrade to 33, but I do worry that this might randomly happen again. If it does, at least I know what to do.