Unfortunately restic was a no go for me due to not being compatible with B2 keys that only have the permissions readFiles,writeFiles,listBuckets,listFiles (no deleteFiles). I don't want the attacker to be able to delete any backups if the manage to get to the B2 keys.
In short, give rclone your keys, (small ~/.rclone config file) tell restic to use an rclone backend and add an extra argument when running restic. (See the blog link above, all explained)
There's an open issue for this which doesn't seem to have moved: https://github.com/restic/restic/issues/2134 - it does have a couple of PRs linked on there which implement proper soft-delete.
I believe this is the ticket that would add support for this to restic: https://github.com/restic/caddy/issues/2