I was considering setting up my #immich server for a while now, but ept putting it off because I thought migrating the photos from iCloud to immich would be hard. Several how to's explained you had to download the photos from Apple's privacy website in bulk, or export them on your Mac as separate files.

So, finally put to work: I made enough room on my Mac to export all of them, I exported all photos in original quality from the Photos app to some directory on the Mac, and setup my immich server.

Then, finally, being able to login on the mobile immich app, I see a simple 'backup' toggle. I can select all albums in the iOS Photos app and switch "enable backups" on.

Just like that, it uploads everything to my new immich instance. This couldn't have been easier. All my prep work wasn't needed.

So, if you have been holding off, don't. This is so easy.