I second this. But keep in mind the difference between a sync tool like rsync, syncthing etc. and a dedicated backup tool like borg.

A sync tool is basically a fancy copy. It copies what is there now. It’s a bit smarter than a copy in that it can avoid copying unmodified files, can optionally delete files that are no longer there, and has include/exclude patterns.

But a sync tool doesn’t preserve older versions, and doesn’t do deduplication, compression, encryption and so on. A backup tool does.

Both can be useful, as long as you use them properly. For example I gave my dad a Syncthing dir on his laptop that syncs whatever happens in that dir, over Tailscale, to my NAS. But the dir on the NAS gets backed up with Borg once a day.

The Syncthing protects against problems like the laptop dies, gets dropped, gets stolen etc. The Borg backup protects against deleted and modified files. Neither of them is of any use if the user didn’t put something in the dir to begin with.