CD Projekt Red wrapped up The Witcher 3 with the Blood and Wine expansion in May of 2016, and while they've still released patches to fix glitches and problems and such, the team has since moved on to work on their other projects, specifically Gwent and, of course, Cyberpunk 2077. But there are still plenty of hardcore Witcher fans who would like to see the company return to the series that put them on the map in the first place, something like a Witcher 4.
Well, good news and bad news, fans, but we'll start with the latter: according to CD Projekt chief executive Adam Kiciński, the team has no plans to make a Witcher 4, as Geralt's story arc is finished and his story has a definitive end. There's no point in continuing it.
That said, here's the good news: he did leave things open for a spot of hope. He continued to say that his team would likely revisit The Witcher world, possibly as a spin-off with a new cast of characters, in order to keep fans (and investors) happy. While he gave no solid details, it's still fairly welcome news for fans. Also in the interview, he also talked about Cyberpunk 2077 and made some fairly boastful claims about the title, such as it would be much bigger in scope than The Witcher 3, and, he hoped, more successful.
It'd be easy to call that a case of No Man's Sky-ing it up, but when the developer behind The Witcher 3 says it, I can't help but believe it.
Anyway. I'd suggest you read the interview yourself, but it's on IGN and in Polish, so this is operating on a translation done over on Resetera. Check that out if you want. They also talk about Gwent, but I omitted that because I think we can all safely assume we knew they'd still be working on that.