Funny how Sony managed to deliver games consistently with their studios working with contractors and also using their own custom engines. Here's a list of studios that have delivered games since 2020 using their custom engine:
- Bluepoint
- Guerrilla
- Insomniac
- Japan Studio / Team Asobi
- Naughty Dog
- Polyphony
- Sony Santa Monica
Insomniac will probably have 4 AAA games released in 3 years using their own game engine. As a matter of fact, the only game from a Playstation Studio that released using an "industry standard" engine was Returnal.