I’m stunned that you are unfamiliar with the versioning feature of backups. In my bubble this has been best practice since Apple came along with the Time Machine, but really we tried that even before with rsync, albeit only with limited success.

This is different from git because this takes care about all files and configurations, and it does so automatically. Furthermore it also includes rules when to thin out and discard old versions, because space remains an issue.

Synologys backup tool is quite similar to Time Machine, and that’s what I am using the second NAS for. I used to have a USB hard drive for that task, but it crashed and my old Synology and a few old disks were available. That’s better because it also protects against a number of attacks that make all mounted paths unusable.

Git is not a backup tool. It’s a versioning tool, best used for text files.