https://wccftech.com/the-witcher-3-xbox-game-pass/

The Witcher 3 is apparently coming to Xbox Game Pass in the future.

An ad that is being shown recently on Twitch shows several games currently available for the Xbox Game Pass, including Gears 5, The Outer Worlds and Devil May Cry 5 as well as The Witcher 3, which is not currently available for the service. This likely means that the game will soon be made available on the service.