Just got a new Xbox One S for Christmas, and I'm now curious to know whether there currently exists a Game Pass for TSW 2020.
Sadly not. TSW2020 is not included in The Game Pass, you have to buy the full game at XBox Store: https://www.microsoft.com/en-us/p/train-sim-world-2020/9p32wwj0pjjk?activetab=pivot:overviewtab