I’ve seen a few people put their delivered pizza in the oven after everyone grabs a piece to keep it warm. I’ve also seen a lot of those people forget the pizza is in there and either have to throw it out or only noticed after they preheated their oven.
Cardboards are actually quite good at heat insulation. If you have an electric oven (no flame) and put the temperature below 200°C (ignition is at a slighly higher temperature but oven aren’t precise), there is no risk. So you can totally reheat pizza at 180°C on its cardboard.