An upcoming Xbox Game Studios game that has been confirmed multiple times to be coming to Game Pass is Undead Labs' State of Decay 3. On Monday, however, it was confirmed that the studio had been sold to another (as yet undisclosed) publisher, and apparently the deal includes details regarding Game Pass.
Game File has now revealed that State of Decay 3's inclusion on Game Pass is no longer certain, as the acquisition gives the new owner the option to not release the zombie-themed game directly to the subscription service. This doesn't necessarily mean it's completely off the table, and the new owner may very well think it's a good idea, but we no longer have any guarantees.
So, we'll just have to wait and see. The game is set to launch next year, so we shouldn't have to wait too long for an answer.