If you go to a route, then timetable, then services, then pick the train, then view services and back out to the route selector, you can't select another route. All you can do is go to Dovetail Live, the store or quit the game.
Can I ask what version of Xbox you are playing this on? I had a very similar problem with my friends Xbox Series X. As soon as you go back to a previous menu your stuffed. Unable to select anything apart from Dovetail Live or Store.
I 've recently purchased a Series S and installed just TSW2 and it works fine, however on the Series X it still has this same menu selection bug. The only difference between the 2 Xbox's is the series X has TSW2020 installed as well.
Odd since my XB1X doesn't have TSW2020 installed. What DLC from TSW2020 was there from release as that could be the issue