Backblaze B2 is their generic object storage platform similar to S3. You pay what you use and it scales into petabytes. There's no minimums so if you're only using small amounts, you get a small bill at the end of the month. It's not backup software, just the underlying cloud storage platform.

B2 is not Cloud Backup, B2 is there S3 compatible storage that you pay by the GB

your links are to their "backup" service which is only for Windows and Mac computers, and is limited to their backup app which many people report having throttling and other issues, it is "unlimited" in the sense that it should only be used for a single computer, which is why they never support Linux on it, because they believe (probably correctly) that linux support would mean most people will install it to NAS devices and ruin the business model for everyone else

Historically that has been the case for all of the backup solutions that offered "unlimited" data for a fixed price monthly, I think BackBlaze is the only remaining vendor in the game that does

Cloud backup != B2.

https://www.backblaze.com/cloud-storage/pricing

$6/TB/Month. Very manageable egress-fees. If you're using it for cold-backup, hopefully you rarely have to pay them.

If Hetzner storage boxes work for you, that would be less than 4 euros per month with unlimited traffic. Next level up is 13 euros for 5TB. (It works fine with restic over ssh but also has options for samba, webdav etc in addition to borg server. Now that I am looking at the info page, it seems restic is listed now too but I am not sure if it's via rclone . https://www.hetzner.com/storage/storage-box )

No egress fees if you aren’t downloading more than 3x what you’ve stored!

It says it can backup my PC but then says it needs windows? I can’t see a “personal” option for other OSes on a PC

PC tends to refer to “not mac”

I’ve been using it on MacOS for years. Works great.