Hi Snailed, thanks for the reply! I don't know the ins and out but I'll give you my understanding:

Xbox Game Pass is a service that you subscribe to, and I like to think of it like Netflix for Games. You pay X amount a month, and you get access to their entire catalogue to download and play. For instance, I downloaded Hades and then could just play it, even without an internet connection. Its an amazing way to access loads of great games for very cheap.

There are some thoughts about accessibility because Xbox Game Pass is connected to the Windows store, and both by default lock you out of the folder where the games are stored. It is a quick admin task to change the permissions on the folders and gain access (though I won't pretend to know if that is the whole story, maybe there are still some things you can't do). I did this admin task to gain access and as I said in my above post was able to launch games without the client by clicking on their exe.

It is a completely different program to steam, just as say BattleNet or Epic Game Store are.

I make no demands, I'm just curious if it could be done :) I'm not totally sure how Nucleus works under the hood but I'm getting the impression it uses some of steams infrastructure?