Here's more prep!
6... b6 shows a complete misunderstanding of the position. 6... Ne4 is premature but playable, but then you follow it up with the terrible b6 move. The a-pawn is a huge weakness that should cost him the pawn. Black should never allow white to simply trade it off.
Black should simply play the natural developing move 6... e6, followed by Bd6. Note that black is in no hurry whatsoever to take that a-pawn, it will fall of its own accord in due course. White will never be to develop their queenside without letting that pawn go.
Here's more prep!