I used to say restic and b2; lately, the b2 part has become more iffy, because of scuttlebutt, but for now it’s still my offsite and will remain so until and unless the situation resolves unfavorably.

Restic is the core. It supports multiple cloud providers, making configuration and use trivial. It encrypts before sending, so the destination never has access to unencrypted blobs. It does incremental backups, and supports FUSE vfs mounting of backups, making accessing historical versions of individual files extremely easy. It’s OSS, and a single binary executable; IMHO it’s at the top of its class, commercial or OSS.

B2 has been very good to me, and is a clear winner for this is case: writes and space are pennies a month, and it only gets more expensive if you’re doing a lot of reads. The UI is straightforward and easy to use, the API is good; if it weren’t for their recent legal and financial drama, I’d still unreservedly recommend them. As it is, you’d have you evaluate it yourself.