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.
3 full backups minimum, one off site. Also handy to grab a disk image occasionally just in case.
I personally never bother with disk image or backing up the OS for my own stuff. I find that usually by the time I think its time to restore a bunch of data my Linux install is full of kludge and crap so easier just to reinstall the OS and then restore the configs and data from backup. That is also when I’ll usually look at playing with another distro. Keeps me learning new things.
Now things like VMs are a different matter and I’ll usually back them up completely.