Witcher 4 is a game that is pushing UE5's limits. Unreal comes with its source available, and CPR had to write their own world partition streaming engine, create a new type of non-actor asset for environment art, introduce a lot of multi-threading improvements. That's why it serves as a good tech demo source. Lots of people in the industry are looking carefully at how this move from a proprietary engine to UE is going for CPR, and this kind of tech demo serves are great marketing towards other companies with an in-house engine considering a move to UE.