There are trains every 2 hours from Zürich to Salzburg. They follow the route: Zürich - Innsbruck - Salzburg - Vienna. This is a scenic route, you see lots of mountains , and follow the valley of the River Inn.
Informations about these trains, including photos of what you see, and a video, is here: https://www.seat61.com/international-trains/trains-from-Switzerland.htm#Switzerland-Vienna
This route does not go via Füssen. Füssen is on the other side of the Alps, in Germany.
Getting from Zürich to Füssen is not easy. The rail line to Füssen runs from Munich south to Füssen and terminates there. From Zürich you need to take many trains and it is a slow route. And from Füssen to Salzburg you have to first go back north to Munich, then east.
- So you have a choice, the scenic route via Innsbruck, on the same train.
- Or the much slower route, with changes of train and doubling-back, to go via Füssen.