It's meaningless bullshit if they think the AI companies give a shit about copyright
Even moreso: When you post online you typically give the website a license to distribute the content in the terms and conditions. That's all the license they need, it doesn't matter what you say in the comments.
There's different kinds of backups. For this you don't need off-site storage.
For this I set up zfs auto snapshotting which means when I delete stuff it isn't really deleted because a snapshot is still pointing at it until it rolls off the time window.
Both zfs and btrfs can do this but you do need to change the filesystem to use these which can be a lot of work.