Maybe this isn’t new and I just missed this before. I did a Bing search for Minecraft Dungeons and one of the top results on the page was a link to play the game on Xbox Cloud Gaming. This is the kind of feature that Google talked about with Stadia and I never saw it happen.
It wasn’t just Minecraft Dungeons, either. I tried several games, even obscure ones. If it’s in Xbox Cloud Gaming, it should pop up. Great feature and a clear statement that cloud gaming is a priority for Microsoft.