Not a lot has been confirmed for The Witcher 4, but Geralt’s voice actor, Doug Cockle, has confirmed that the protagonist of CD Projekt Red’s Witcher trilogy will come back in some form for the latest game. With Ciri being the protagonist, it means that his role could be anything from a small cameo, like Letho in Wild Hunt, or a larger mentor role, similar to Vesemir. Although one of The Witcher 3′s endings is clearly canon now, with Ciri becoming a Witcher, it isn’t as clear as to which of the other choices are also canon.

https://screenrant.com/witcher-4-geralt-relationship-yennefer-op-ed/