Best scenic route starting in Vienna through Austria and Switzerland mountains

Sounds like a plan. There is even a direct train from Vienna to Zürich that you could take until Sargans. (that way you only have to change trains once).

Switzerland also has a lot of scenic train routes starting arround Chur. (The Narrow gauge (1m) railways of Rhb for example, like the Bernina line)

​@jammymummy 

From June 14 to October 14, 2026 the line between Feldkirch and Buchs will be closed due to engineering works. Replacement buses will be provided. You should plan more time and a second change in Feldkirch. Some trains will be rerouted and will stop in St. Gallen, from where you can also take a train to Chur.

The closure of the railway line through Liechtenstein (Feldkirch in Austria to Buchs in Switzerland) this summer was already mentioned by ​@jammymummy . The direct trains between Vienna and Feldkirch (or Zürich, if the line is open) do not go via Munich but via Rosenheim in Bavaria (they do not call there, but bypass the station). If you do not like to use this connection a quite scenic but longer alternative (10 hours instead of between 6 and 7) to Feldkirch is Vienna – Semmering – Leoben, then to the Enns valley at Seltzthal, from Enns valley to the Salzach valley at Bischofshofen and then via Zell am See to Wörgl, where you reach the line used by the direct trains. With the changes in the timetables after the opening of the Koralm tunnel you will have more changes of trains than before, but it is still possible.  Decent route planner, e.g. from ÖBB or DB, will give you some connections when searching for Vienna to Feldkirch via Leoben. An additional via Zell am See will exclude connections via Salzburg and Rosenheim.