The simple editing of a non-steam game steam library shortcut with launch options and app id is all that is needed.
Not sure if simply linking Steam account to Xbox app on windows account for games that you already own (bought from MS store) is key to a better working solution for adding games you already own to Steam Library as a non Steam game so appreciate this guide needs updated. UPDATE 7th June 2021:Valve have added Xbox Games Studio games to Steam Store which gives better support for Steam client features, so being able to buy Xbox Games from Steam Store for better support of Steam client features should be highlighted due to the caveats of adding UWP/Xbox Games Pass games to Steam Library as a non Steam game.