Only so much can be learned during the NFL preseason. Teams approach each game with vanilla schemes; there isn’t a full weak of opponent specific film review and planning; every projected starter or role player who has a paper cut is held out or severely limited for these games; and so on.
One area of the game that doesn’t change much is what happens in the trenches. Offensive and defensive linemen won’t purposely change their technique, their assignments, or even their intensity and effort level. This is a dress rehearsal in the realest sense for offensive and defensive linemen.