It’s been about 18 months since I last tried to use Proton for photo backup, so maybe things have gotten better. Proton Calendar certainly has. But at the time, it had no support for searching, tagging, or location metadata, didn’t respect existing albums, picture previews were unusably slow (maybe because of encryption, in which case, fair I guess) it didn’t let you select what folders you wanted to update (so instead of just backing up my camera photos, it would back up downloads, screenshots, memes, etc.). It lacked the ability to select all or groups of photos, even just straight uploading would be painfully slow and fail frequently.