I set up immich backed by ceph last week and I got everything migrated via immich-go, with all metadata albums and all.
Had to change some parallelization option, but otherwise it was a breeze.
Besides, having to use external tool you check out from GitHub is the exact opposite of what should be the priority I am talking about. Immich gives you that clean, very easy UX/UI, targeting every regular user as a real alternative to Google or Apple offerings, yet you can't easily and safely import your photos. That's inconsistent at best. Misleading.
How do you imagine this wold work, given that there are no APIs for Google Photos or iCloud Photos to batch import them into a different service while preserving all data. At best you can work with the Gallery/Photos access on your phone.
The way it CURRENTLY already works. Through Google/iCloud takouts, or the Android/iOS apps if user chooses to do so.