Generally, no, you do not need to "stamp" or validate Swiss train tickets in a machine before boarding, which is a relief compared to Italy or France. In Switzerland, tickets purchased online, through the SBB app, or at a station are already considered valid for the date and route specified. If you are using a Swiss Travel Pass, you simply show the QR code on your phone or your printed pass to the conductor during their ticket check. The one exception is the Swiss Travel Pass Flex; for this, you must "activate" your specific travel day on the website or app before boarding your first train of the day. Once activated, your digital pass is your validation. Always ensure your phone is charged, as a dead battery is not a valid excuse for not having a "validated" digital ticket.