FlyerTalk Forums - Passing through Austria on a train OK?

There is a night train from Zurich to Prague that would be perfect for a trip I am planning in August which is needed to complete some unfinished business that was meant to be done in May.

There are currently no restrictions on UK travellers going to Switzerland or Czechia, but this train passes through Austria for most of the journey and UK travellers are supposed to have a negative test in order to enter Austria or quarantine. However there is an exemption for transit. Do you think this train journey would count?

I'm not intending to get off in Austria but I wonder if/how they are enforcing this requirement given that the passengers on this train would mostly be expected to be Schengen residents who are (with I believe the exception of Sweden) currently allowed to go to Austria with no restrictions. Will Austrian police be waiting at every stop in the middle of the night to see if anyone unauthorised disembarks?

Also can anyone make sense of the message on the home page of https://www.nightjet.com/en/

I did some dummy bookings and the only available tickets are in a 3-bed shared compartment (at the expected price for 3 strangers sharing), which would obviously be irresponsible of them to offer at the moment - it won't give a price for a solo cabin, so do you think I should take it that if I booked the 3-berth compartment they won't put anyone else in it?