This is symptoms of a chronically cloud-native brain. What is a file system?

The immediately obvious and simple to handle on-disk format for everything I cared about was one of the things that convinced me to give it a try. Well-crafted exporters are great and all, but I really like being confident that I can convert it by hand even if the company ceases to exist.

Backups are easy too: you can very reasonably just rsync the library folder, and it'll be recoverable from that alone (I tried it! Worked great). You'll lose accounts and image-content search and iirc faces (possibly painful), but most of that is trivially rebuilt or not very interesting for single-person scenarios.

It's tricky with iOS. Plugging iPhone into a server is stupid. Adding server as a network storage in Files app is smarter, but downloading photos this way does not guarantee deduplication. Would be great if Immmich iOS app had a restore functionality as convenient as existing backup functionality.

You migrate from the server, not the client. You seem confused about what Immich is.