It copy Photos, iCloud files and my mails once every days to S3 with incremental backups.
It requires to have a full copy locally.
Works great!
It is not hard to configure once, with the proper folders and settings.
yeah that's the thing. When my iPhotos library exceeded 1TB I lost the ability to store the full local copies. Since then, iCloud itself has been the sole source.
Looks like there's some decent, reasonably priced apps to handle this like https://apps.apple.com/us/app/parachute-backup/id6748614170?... (no affiliation)
I wonder if it can calculate (estimate) how big of an external disk I'll need. My wife and I each have 40-50k photos and a few thousand videos in iCloud Photos.
Even doing this yearly can save the immense sadness of lost memories. And of course, this works for emails, and everything else.
If you encrypt it, make sure you use a method not tied to any external service, or the machine you're on. I don't use Apple, yet I suspect that an encrypted external backup might be tied to your Apple ID, or some such, because that's how the world flies today.
I wouldn't bother to encrypt, it's just family photos and I wouldn't want to complicate restores. Especially if it was my wife who eventually needed to use it.
Weirdly, that number is different than Immich’s estimate of my photo library (95 GB vs 150 GB), but perhaps good enough to get you in the ballpark.