other than inflation rooms
Oof, there really aren’t any games, outside of some niche Flash games I’ve seen quite a long time ago that I can’t find anymore. 99% of all p-balloon content has been animated and not interactive, though.
It’s not actually using P-balloons, but | [Game] Bakery Bloat-Out~ (V1.5.3) | by SquishySofty on DeviantArt gets the shape at least.
Outside of Super Mario World and Super Mario Maker 2? I can’t really tell unless it’s a ROM Hack of the game that has the aforementioned power-up (outside of choice ones that don’t have the playable character inflate) or a fangame inspired by the latter game that hasn’t been taken down by Nintendo’s litigation ninjas.