Photos migrating to MacBook

What I am not understanding is you say you transferred 19000 photos - were these in the photos library? Viewable when you open the photos app?

Or were they individual image files in a folder?

Then after you transferred the library it synced again with iCloud - and that took a long time - Correct?

If that is now complete then there is nothing else to do. However if the sync has only just started and is taking a long time, you could choose just to create a new empty library, and sync that with iCloud. This is quicker than a sync of a full library, but still quite slow. So if the full sync is more than half way though, probably not worth starting it again.

What do you mean by "migrated from iMac"

Have you copied the library over? Where are you downloading from?

How long have you currently been waiting. How large is your library.