Good Point. The purpose of classification is too communicate what information requires limited access. Information can not be declassified without specifically identifying what is be declassified. Since presidents are not required to sign out classified documents, saying all classified documents at Mar A Lago are declassified is meaningless. Clearly, Trump was attempting to cover his ass, not to actually declassify any information.
You said, " Information can not be declassified without specifically identifying what is be declassified."
And that is obviously wrong.
First of all, identifying what is to be classified or declassified would require creating an additional classified document.
You never want to do that. You are not supposed to say why a document is supposed to be classified or not.
That would be like creating a guide for spies as to what they should steal and what to ignore.
What is done instead is to blanket classify the entire document. It is marked on each page, even if that page is benign.
Saying all documents at Mar-a-Lago are declassified is not meaningless, because as president when the docs were made, Trump has full access to them and can copy, keep, or destroy them at will.
He can also employ trusted employees to help, at will.
The problem is not about classified docs.
The ONLY problem is if he is trying to sanitize and prevent harmful docs from getting into NARA.