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.