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.
I self host an instance of nextcloud on a headless machine in my home. It gives the benefits of typical cloud based services, but you control the storage. And if you sync with at least one other machine you have a full backup besides.
Of course no solution is perfect. This requires extra time, effort, and hardware. And having my data in one physical location has it's own risks. But I still prefer it.
So, something to consider if you or whoever is reading this isn't aware of that option.
If you have any friends or family in a nearby town, ask if you can leave an external hard drive at their house. You could make a full disk encrypted backup of your machine every week or so and then when you visit them leave a copy of your backups. It may give you more peace of mind if the data is valuable like journals or family photos.
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.
My condolences on your lost data. That must have been a horrible realization.
I've also learned the hard way to keep all my important documents on Nextcloud which is completely synced to my desktop and laptop as well as backed up to another server with Borg. I also backup the ephemeral local files (screenshots, wallpapers, programming stuff) from my SSD, again with Borg to that same backup server and an external hard drive.
Always always always have 3 places where you store your data. Your main data store. Another storage location and then one offsite. And like others have said...check your backups occasionally to make sure you can successfully restore from them.