According to this, it isnt so black and white.
Former President Trump claimed documents found at Mar-a-Lago were “all declassified.” We explain why sitting presidents can declassify documents and how it works.
www.verifythis.com
He can basically do whatever he wants with declassification. There are informal protocols, but nothing set in stone. EXCEPT nuclear documents. Those are protected under the Atomic Energy Act.
Apparently, just because they are declassified, doesnt mean they can just take those documents with them when they leave the WH either.