Diablo IV is releasing on June 5th, 2023, at least according to known leaker Aggiornamenti Lumia who has a history of pulling information from Microsoft servers.
There have been many rumors that Diablo would show up at The Game Awards on December 8th, and it makes sense if a release date is revealed there. If this date is accurate, it increases the likelihood that the game launches day one on Game Pass, assuming the proposed Activision-Blizzard acquisition goes through before then.