Yeah, Android without root doesn’t have to many options for backup. And still, the backup options available are like… outdated? A little weird to work with them, that’s for sure. But since you can backup all your pictures using the Google Photos and use Drive to backup your settings, I think maybe developers don’t see the point. Personally, I don’t backup my phone. I just backup the pictures and Google Photos is nice for that but the downside is that if you opt for storing the original pictures then it takes space from your Drive and if you decide to use the “unlimited” option, then you lose the original resolution.
It would be great if someone decides to develop a restic frontend for Android, but I’m no developer or anything related; just another user.