It's not on GamePass and it doesn't need Xbox Live Gold either. MW2 and its multiplayer component⚾️ is not free. You need to buy it if you want to play the single player game or MW2 multiplayer.⚾️ You should be able to delete the campaign if you don't want to buy it.

If you will be playing the game campaign for the game no need⚾️ for an Xbox Live Gold, you just need to set your console to offline. To do so please follow the⚾️ steps below: Settings > General > Network Settings > Go Offline.