iCloud

This article https://www.heise.de/news/iCloud-Daten-Mac-App-sichert-Drive-und-Fotos-10508960.html (for macOS, behind paywall and in german) describes some options like
https://www.parachuteapps.com/parachute
and
https://support.bombich.com/hc/en-us/articles/20686419951767-Backing-up-the-content-of-cloud-storage-volumes

Currently we have no Apple devices to try them out ourselves.