CDPR recently unveiled a new Game for The Witcher and said it will be made using Unreal Engine 5. Recently, a former CDPR employee said that the new Game of The Witcher moved to Unreal Engine 5 development, possibly because if you use the RED engine to develop, you need to rewrite the engine.
Bart Wronski, who worked on graphics and engine programs at CDPR, said on Twitter that CDPR had to rewrite the RED engine every time a new game was developed, including almost all of the core underlying systems. This has been the case from The Witcher 2 to The Witcher 3 to Cyberpunk 2077.
If the new The Witcher game were to be developed with the RED engine, it might be the same way, as Cyberpunk 2077 doesn't have a Wizard 3 system. He also thinks it would be better to use Unreal Engine 5 because it has a mature foundation. Gameplay and open-world content are to be remade anyway, but the team doesn't have to spend a lot of effort updating engine tools and features anymore.
For the switch to Unreal Engine 5, CDPR officially said that they have opened a multi-year strategic partnership with Epic Games, with the main goal of adapting the co-engine to the open world play experience, and working closely with the developers of Epic Games.
At present, CDPR has not released detailed information about the game, such as the development time frame and release time.