Ckoumaisouwh62
My understanding is that if you have Swiss TRAVEL pass, no seat reservation is needed unless it is explicitly required due to high demand or specific route. You should be bale to see the recommendation in the SBB app.
For example, I reserved a seat in the Panoramic train (Interlaken Express) because I wanted a specific seat and my family to be together I paid the extra reservation fee but my Swiss Travel Pass covered the ticket fare. Afterwards, I was told I could have very easily just boarded the train and looked for a non-reserved seat and sat down because I had the Swiss Travel Pass that was valid for a period of time (non-flex).