These types of compilation movies are typically just the series edited down to fit the runtime of the movie(s). Sometimes, they will include a new scene here or there, but it usually is pretty minor or just a slight change to make it flow better with the editing for time that was done. I have not seen any announcement that these will or won’t include any new animation, so place your bets now.

I expect there might be an announcement about more Bocchi seasons either at Anime Japan in March (she was in the visual they released) or after the studio is done with these movies.