Biden's staff found a handful of classified documents mixed in with 1000s of other papers, and returned the documents immediately.
Trump took boxes of classified documents, refused to return them after receiving a subpeona, then returned some while claiming that all had been returned. He hid the remaining boxes, which required an FBI raid to secure.
It's not unusual for a Trump supporter to not know the basic facts of a case. That's why they're a Trump supporter.