You can do this with GloSC/GloSSI (the latter is a newer rewrite of the same tool). You can add any UWP app (including the Xbox app itself) to Steam with it. When you run the new ‘Xbox’ entry in Steam GloSC/GloSSI will open in the background and launch the associated app, and a virtual controller will be detected, which every game will see as a generic physical Xbox controller. GloSC/GloSSI then translates your Steam input to the virtual controller, avoiding any associated compatibility problems. I would suggest binding the trackpads to a mouse for easy controls, and also configuring Windows to automatically open the on-screen keyboard when typing, sleep on the power button and not show a lock screen on wake so it works just like SteamOS.

It can also create overlays for the Steam Big Picture UI allowing you to create a SteamOS-like experience, but I find it a bit inconsistent so YMMV.

Basically, install GloSC/GloSSI, use the app to add the Xbox app to Steam, and bind your controls for it in Steam to an Xbox controller.