After a single APT command gone wrong made my Debian installation unusable, I decided to reinstall Linux. I tried to back up everything to my external hard drive, but it kept unmounting, so I elected to use Filen (a FOSS cloud storage provider) instead.
It was only after installing openSUSE Tumbleweed with KDE Plasma that I realised I hadn’t actually synchronised the folder I had moved my backup to; meaning I have lost everything but a single Minecraft world (which I had backed up to a Compact Flash card in February).
Tl;dr: Double check your backups, and use physical storage whenever possible.
Welcome to our exclusive club :)
It does suck, I feel you. Lost every single photograph I took in the early 2000s back around 2008 because of a failed hard drive that I never backed up. I have five backups now that I test regularly of all my personal data.