Over the internet for file sync. Desktop devices.

I heard good things about Newsblur. They offer a service and an open source version for self hosting

https://github.com/samuelclay/NewsBlur

This is a great hint, thank you. I just discovered that the official restic docs recommend this method too

Thank you!

https://restic.readthedocs.io/en/latest/080_examples.html

This might be a good idea. It would only work for files that allow read access for the group, but that should be fine

Restic uses smart Delta backups, creating a tar before the restic process would defeat the purpose. The permission issue is the same, as I need to have access to the Files either way.