Hi
It's possible that people just don't know if it's possible since the gamepass version is so new, and if I remember right packaged differently than non-gamepass versions. If you have C:\Users\user_name\MyDocuments\MyGames\BattleTech\mods as a directory you should be able to use the built-in modloader for some of the more basic mods. Though that has some limitations as iirc large mods (like for example RogueTech and BattleTech Advanced) don't work with it and require modtek. Which if you can't inject modtek into the game then using modtek is not possible.