If you can solder I’d say most mice are easily fixable. The most common defect for mice are the switches, which are usually quite simple to desolder, as there aren’t any components near them.
E.g. I don’t have much experience soldering and it took me under an hour replacing both switches on the G Pro Wireless as well as the battery. I’ve bought this mouse used about 5 years ago and I wouldn’t be surprised if it lasted another 5 years.
Edit: The annoying part is the screws being below the feet, so you have to replace them after opening the mouse. But it’s all screwed in.
I also wholeheartedly recommend Restic. Hetzner Storage Box or Backblaze B2 are great storage backends and directly supported by Restic.
Borg is great too, though I’ve never used it because I’ve discovered Restic first.