Hello Robilo
A ticket does not grant you a free seat, it grants transportation, however.
We use our trains like buses: hop on, find yourself an empty seat, have a ride, hope off. Your Swiss Travel Pass allows walk-in, without bothering yourself about the purchase of tickets.
On certain train types you can reserve a seat, which is totally optional (most Swiss people never reserve a seat) read here:
https://community.sbb-tickets.cc/blog/23887-demystifying-seat-reservations-on-swiss-trains-a-comprehensive-guide
The red plastic card is given to residents only. For you, it is sufficient to show the QR code in the SBB Mobile app together with your physical passport (no copies, no images of it on a smartphone).
I an on a train to Interlaken. The train is well booked, a lot of tourists going to see the beautiful snow-caped mountains. Nobody reserved a seat, all are happy. Everyone has shown their Swiss Travel Pass as I instructed above.
Kind regards,
Roland
