I use rsync for that.

As does syncthing under the hood. The issue is with backing up an open database and getting an inconsistent state, but KeepassXC keeps its database closed except on update. I also tick the backup old before save setting in KeepassXC (the aforementioned ‘and it’s backup’) and use a versioning backup of the sync directory on the desktop with 3-2-1, so I am sanguine.

Syncthing means it and its backup lives on two laptops, a desktop and my phone.