Hello 史瑞克
Thank you for your request.
Yes, that’s correct. The Swiss Travel Pass is valid until Domodossola. For the rest of the trip, you need an additional ticket. I also advise you to check whether seat reservation is mandatory on your train, as it is not included in the Swiss Travel Pass.
Under this link, you will find more information about the Swiss Travel Pass and its area of validity: https://sbb-tickets.cc/en/leisure-holidays/travel-in-switzerland/international-guests/swiss-travel-pass.html.
I wish you a nice afternoon.
Best regards,
JulieL