I (non EU resident, vaccinated outside EU so no Green Pass) was planning to visit Switzerland, Austria and Hungary this month, traveling by train. Looking in Google maps, I saw that the train from Zurich to Salzburg crosses the border with Germany. Would I need to comply with the German COVID entry restrictions (entry form, etc), or those wouldn't apply to train travelers for which the final destination is Austria?
The RJ between Zürich and Salzburg runs through Germany as a corridor train. That is a train that runs through a foreign country without stopping, with the special privilege that the passengers on board do not have to pass border formalities.
There is an interesting article about those trains here:
Austria now has pretty frictionless borders with all eight of its neighbours, all of which are members of Schengen (the last to join was Liechtenstein in 2011). But in the second half of the last century, frontiers were firm and the Austrian Federal Railways (ÖBB) secured privileged transit rights for its domestic train services to cross Germany, Italy, Hungary and Yugoslavia in order to link Austrian communities along the border. To this day, the hourly Railjet trains from Salzburg to Innsbruck still run non-stop through a 115-kilometre corridor of German territory.
As a result, when you are on that train you do not officially enter Germany, and are thus not subject to German entry requirement.