Assuming you have a local backup too, rsync.net is an interesting option. It even supports ZFS snapshots natively if you're using a NAS. In case of ransomware it's useful to have access to older snapshots.
Myself, I keep everything on my cheap surplus NAS (2 drive redundancy), snapshot regularly, and occasionally sync to an airgapped drive the next town over. I keep a cold copy at my parents house, but that's last-resort.
The important bit is that I've successfully trialed recovering from a total loss of my NAS and house, in case that ever actually happens :)
Frustratingly, the Backblaze personal backup client doesn't support Linux, because they don't want people to abuse the personal backup service for their server, NAS, etc.
Myself I pay for Backblaze's Personal backup solution.
There also is Backblaze's B2 Cloud Storage (free 10GB tier) if you want something similar to S3.