You might have local backups on your MacBook. Those take up space but aren't reported by Finder. If you have both iPads, you can transfer directly from one to the other during setup, without using the Mac at all.
I've deleted all iOS backups as able to via the Manage Backups option, I've also looked and delete current time Machine local "backups"
I actually TM backup to a TrueNAS Core.
Space can't be the problem... but then it also don't give you much information into what where how...
G
You might have local backups on your MacBook. Those take up space but aren't reported by Finder. If you have both iPads, you can transfer directly from one to the other during setup, without using the Mac at all.