(Don't ask me for a source, I don't remember where I saw that info)
How sure of that are you?
There are several reports that the sequel to Cyberpunk 2077 will be using UE5 as well.
As in, CD Projekt Red have purposely switched all future projects to UE5.
* https://screenrant.com/cyberpunk-2077-phantom-liberty-dlc-la...
* https://kotaku.com/cyberpunk-2077-phantom-liberty-expansion-...
Unless of course something changes during the development of the next Witcher game and they decide to go back to RED Engine.
(Don't ask me for a source, I don't remember where I saw that info)