I’m not sure how funny this will be, but here’s how I broke my system twice in a single case. Step by step:

1. Migrated from Manjaro KDE to EndeavourOS KDE. Kept the previous home directory.
2. After a few updates, there was a problem with Plasma. Applications were not starting from the panels or the .desktop files (they worked from the terminal. The terminal emulator was in startup and worked that way)
3. After a few google searches, found out that downgrading glibc would do something, so downgraded… Worked for a while
4. While using pacman -Syu, I always checked for warnings (foolishly thinking that the downgraded and ignored glibc would cause a pacman warning if it broke dependencies) and there were none. So, the updated OS stopped working due to unmatched glibc. BREAK 1
5. To fix it, I opened one of my multiple boots (another EndeavourOS) and made a script using pacman -Ql and cp to copy new glibc related files into the broken system (because I was too lazy to learn how to do it the correct way with pacman and chroot didn’t work because glibc is needed by bash).
6. Turned out the script I made was wrong and I hadn’t checked the intermediate output from pacman -Ql, which was telling cp to copy the whole /etc /usr and other directories. (just if I hadn’t given the -r to cp) BREAK 2

In the end, I just made a new installation, this time with a new home and hand-picked whatever settings I wanted from the previous home, Viva la multi-HDD