I’m setting my new MacBook from scratch. I typically have no trouble with this except for migrating my photos library. Almost every time I’ve copied Photos Library.photoslibrary to a new machine I get Photos.app uploading every photo to iCloud to validate it. My library is 100gb+ so this takes forever. Once a couple years ago I copied the library to a new machine and Photos.app was immediately happy - no validation uploads at all!
I don’t know what I did right in the case when my whole library didn’t need to get validated with iCloud. Any hints on how to get that to happen again?
I have never used it, but PowerPhotos has a really good reputation with dealing with the Photos library. You might pose a question to them if their software would make your migration easier.
From memory it doesn’t upload every photo but it does check every photo. So while it won’t use a lot of bandwidth, it will take a lot of time.
@jellis have a read of this post from a friend of mine and see if it helps. It’s a few years old so some buttons will have moved etc, but the principles should still apply.