I had backblaze, and it’s really a bummer they don’t support linux. The closest one I’ve found is Icedrive, but it costs a bit more. I don’t mind paying a bit more though for a FOSS solution (technially not free but yeah). I probably only have 2 TB of actual important stuff but it would be nice to have more for future.
I’ve been pretty happy with rsync.net, with the promo rate I’m on I get 1.6TB for $10/mo. More than enough for backing up my most important files, private keys, camera roll, anything irreplaceable.
The rest of my NAS is 50TB of movies and shows so I’ve just resigned myself to the fact that it will never be affordable to backup more than my user folder.