These documents are Presidential records. Whether classified or not, Trump has no right to keep Presidential records, as per the Presidential Record Act. As I replied to you before, It's not the FBI, It's the NARA which wanted them back.
From a link kindly indicated by your pal Riclag:
"The classification system is separate from criminal penalties that Congress has imposed to protect security secrets. For example, the Espionage Act of 1917 — one of the three laws cited in the search warrant of Mar-a-Lago in Florida — is designed to protect secrets related to defense information that could harm the U.S. or aid a foreign adversary. It makes no reference to materials’ classification status, and prosecutors in an Espionage Act case do not need to prove that materials were classified but rather that they were “closely held,” and their release could damage national security.
The search warrant executed in August at Mar-a-Lago cited as “probable cause” violations of relevant parts of the Presidential Records Act, which does not carry criminal penalties, as well as three provisions of criminal law: a part of the Espionage Act that deals with the mishandling of “national defense information” (18 U.S.C. § 793); a records-related obstruction statute (18 U.S.C. § 1519); and a third that deals with the mishandling of public records (18 U.S.C. § 2071). None of the three criminal statutes deal with classified material per se. Penalties differ. The obstruction-related statute carries the strongest sentence of a fine and a maximum 20 years in jail for each offense."
https://abalegalfactcheck.com/articles/declassified.html
Capice?