Is the Xbox Series X compatible with all old Xbox titles?

I'm considering buying a new Xbox when the Series X is out I also wanted an old Sims title that I used to play on the GameCube and which the original Xbox likes to play.

So far, however, it has not been clear to me from Microsoft's press releases whether the console now supports all old games or just a back catalog like the Xbox one

If any of you are smarter than that, feel free to contact us

Sorry but I don't know the exact details.

But I would guess that it will only be selected games.