It seems Doug Cockle, the English voice of Geralt in The Witcher series since it began, got in some hot water over the comments he made back in August (resulting in articles like this). Cockle claimed that The White Wolf would be "part of the next game" but that the story wouldn't be "about him this time".
That's according to the actor, who commented on the matter in another public setting at MCM Comic Con Birmingham (thanks, GamesRadar+). Cockle previously intimated that Geralt would return in some capacity, but he's walked even that back now, and the actor now claims to know nothing about The White Wolf's whereabouts:
"I did go online, and I said something about this, and then I got slapped by CD Projekt because—I don't know how true it is. I went off a rumour; I thought I'd seen somebody from CD Projekt say that Geralt would be in Witcher 4, but he wouldn't be the main character. I don't actually know if that's true now because they came back and they went, 'We haven't put anything out there, don't say anything!'