They were/are not classified. He was the ultimate classifier/declassifier. He declassified them. He said he was going to do that before he left office. The papers FBI was looking for are likely anything that shows the FBI as the political actor for the Left that manufactured the Russiarussiarussia “investigation.”
Having been surrounded by Top Secret codewords for decades, I felt that much of the information I was aware of was soon dated, and, frankly, much of it was bullroar. What was of concern to the intelligence community was not the information itself (plausible deniability plays a role in its construction) but how the information was secured. Ever since Jimmy Carter ripped the CIA a new one with Stansfield Turner at the helm, Signals intelligence has generally replaced humint, or human intelligence gathered on the ground. And I personally would much prefer to see humint coversheets in the Trump co0llection.
Personally, I understand why such reports would be of interest to Trump. I would think that he, like other Presidents before him, is preparing an autobiography covering his time in office. And I wish him well.
Parenthetically, if on leaving government it was discovered that I had taken some of the delicious cables I can recall, I would go to jail. Thus, I envy the President because he is in the position of declassifying documents, and he can do so for his own purposes — which previous Presidents found no need to explain. Is the FBI on a witch hunt? Damned tootin. However, that patient is so diseased it is quite possible we will never learn the depth of its collective degradation.