https://wccftech.com/cd-projekt-red-switched-to-unreal-engine-5-the-witcher/

CD Projekt Red switched to Unreal Engine 5 for the next entry in The Witcher series to use an engine with a solid base and stop chasing REDEngine's tools and features for each new game, according to a former CDPR employee.

Speaking on Twitter, former CD Projekt Red employee Bart Wronski provided some context for why the studio switched to Unreal Engine 5, revealing that for each new game, the studio basically rewrote REDEngine from scratch, hoping it would work better than the previous time, but then had to hack it due to crunch, which made it not maintainable. As this would be happening again, the studio opted for an engine with a solid base to avoid making the same mistakes of the past.