This is pretty much what I searched for. Thanks!

For backking up files I can recommend restic. It encrypts and compresses your backup. At the same time it does deduplication. So if you backup a file twice, it takes only the space of one. If you are lucky it will even do that for oaets of a file. Although it only has a cli.

Even when they are protected, when did they receive the last update? There are probably so much more vulnerable IoT devices.