When you're buying a Swiss Travel Pass - Flex is a "free day" considered just the days you travel by train or do you have to use up a free day if you're planning to take a bus or tram in Zurich? Are museum visits covered by the pass only available on the free days or can they be visited using the pass any day? Thanks!
ALL coverage and ALL discounts are offered ONLY on the counted travel days with a Swiss Travel Pass - Flex. That tends to make the consecutive-day passes more attractive, this year, if they're a relatively close fit.
This is different from most other passes in Europe, which don't require using counted days to get percentage discounts. But it's typical for fully covered service.
Many cities (Luzern, Montreux) will also cover local buses and trams via a free City visitor card that you get from your hotel, if staying in one. But I don't think that Zurich does the same - they have a City card you can buy.