My computer was taking too long to start up, which I interpreted as failing to boot, but in hindsight was probably just my hard drive being slow. So, I booted into recovery mode, and ran an update. At one point, apt said “there are unnecessary packages” and would I like to remove them? I figured that apt knew better than I did (after all, maybe a package dropped a dependency), so I said yes.
It was after I noticed the very large number of packages that I suspected I messed up. Turns out, apt uninstalled the entire desktop environment, and network manager, so I had to boot into a USB drive with Network Manager installed, chroot into my main drive, and reinstall plasma. As a bonus, I think I missed the main group for the plasma desktop and only installed only most of it, so some of my extensions just didn’t work anymore.
Have you had any luck with hibernation with a BTRFS swapfile? My computer still does not start from hibernation, and I am not sure why, even though I followed the Arch wiki to set it up.