'Plenty' is a loaded word. We're about to find out if it was 'plenty' or not.... but I don't think most would agree that he has done a lot of it, at least recently. When he was at Arizona State, they ran a lot of plays from under center, but at LSU with Brian Kelly it was almost exclusively shotgun and pistol formation. And as we all know, it was very rare for Kliff to have him under center (I'm seeing less than 5% of the time when I try and research it).
I have no doubt Jayden can get very good at doing whatever they ask him to do. But I think it's safe to say he will have a lot of work to do to get as comfortable under center as he has been from the shotgun.