CDPR confirms that a new Witcher game is in development. It'll use UE5 instead of REDengine This new Witcher game will kick off "a new saga" for the franchise .
As for their switch to UE5, it appears that CD Projekt RED is working very closely with Epic
This is an exciting moment as we’re moving from REDengine to Unreal Engine 5, beginning a multi-year strategic partnership with Epic Games. It covers not only licensing, but technical development of Unreal Engine 5, as well as potential future versions of Unreal Engine, where relevant. We'll closely collaborate with Epic Games’ developers with the primary goal being to help tailor the engine for open-world experiences.
At this point, no further details regarding the game — such as a development time frame or release date — are available.
REDengine, the technology which powers Cyberpunk 2077, is still being used for the development of the upcoming Cyberpunk 2077 expansion.
Update on Unreal Engine 5, game wont be an EGS exclusive: