Syncthing is my answer though I appreciate it doesn’t get to the root of your question.
There are local backups that include your system settings, text messages, contacts, call history and (optionally) apps. The one thing I want is the ability to pick a directory for the local backup so I can make it work with syncthing without jumping through hoops.
It’s also compatible with Nextcloud and WebDAV if those are options for you.
It’s been my most used feature on my Garmin Instinct 2X tbh. Glad I don’t have to carry a separate gadget.