As a rule, seat reservation is not required in Swizerland and in many cases not offered at all, only special tourist trains and international trains run with the likes of SNCF are an exception. Even where possible it seems relatively uncommon for people to reserve seats.

IF done at all its always for big groups, school classes etc-when mostly a whole car/floor is set apart with stickers. Normal people do not bother about this

With swiss fares a normal ticket-always in CHF will cost much more as 19 though

In Geneva you will get to 95% easily a seat without a reservation… 2nd August is a Tuesday (ok, Tuesday after holiday but still), so this train is very likely not going to be super busy.

If you look in the SBB app you can see the expected occupancy. On this train the expected occupancy is low to medium, so there will be lots of space.

Thank you very much for all your answers, they are helpful !

This journey does not require an additional seat reservation! It's not really possible to make reservations through our website for journeys that do not require them, but as other members suggested, you can check out expected occupancy on the relevant carrier's website or app before your journey so that you can know what to expect.