Advice on 12 Day Switzerland Trip for first visit

Your itinerary has you changing locations 7 times in 12 days. That is more than I prefer. You will have to get very lucky with weather to see what you hope to see at each stop. Staying in one place longer gives you flexibility if the weather requires you to change plans.

As an example, we spent 5 nights in Wengen in June. Going to Jungfraujoch was a priority, but it was rainy/cloudy every day except one day. We had to look at the weather every morning and adjust plans based on what made sense. Even then, we ended up at First, driving mountain carts in a rainstorm and stuck on the mountain when lightning shut down the lifts for over an hour.

Way too much moving around. Perhaps skip Zermatt, as you will have the ultimate Alps experience in the Berner Oberland.
With the chaos of the airlines post- Covid, you need to build in an extra day at the beginning, in the event your flight gets canceled or significantly delayed. That's happened to us our last 2 out of 3 international flights.
Pontressina is much more charming than the glitzy high-end shops in St. Moritz.
Have you actually blocked out how much time it takes to check out of your hotel, walk to the train station, travel, walk to your new hotel, and check in? You also need a slow down day, maybe you'll have a cold, do laundry, and have the flexibility to adjust for bad weather.
This a is beautiful country and I wish you a wonderful trip!

On top of the other comments, with which I agree:

I would choose between Lugano and Locarno, one is enough. I would probably pick Locarno/Ascona.

And I find the Rhine falls to be totally underwhelming. They're pretty, but there is very little to actually do. You could probably cut Zurich to 1 final night and add time elsewhere.