Maybe he doesn’t have any idea NOW, given his stage of dementia. That doesn’t mean he wasn’t aware when he took them six years ago and hid them in his garage, his office, and his house.I'm still trying to figure out what you think is the most likely issue here.
If you think Biden knew that the documents were in the office, why did he send his lawyer to get them if the lawyer just turned them over to NARA which caused the whole mess?
It only makes sense that Biden didn't have any idea they were there.
The most telling part will be what was IN those classified materials.