Itinerary for 11 nights in Switzerland

You can easily remove Zurich and simplify your stops, as your day trips are easy from Luzern. Zurich isn’t in the mountains and I wouldn’t waste precious days in the city. Here is an option:

Arrive Zurich > Immediately train to Luzern for 4 nights (Day Trips to Appenzell, Bern, Zürich I’d you really want + time around Luzern)

Luzern > Wengen - 3 Nights (more picturesque than staying in Lauterbrunnen and can easily access The Valley + experience a car free village)

Wengen > Zermatt - 2 Nights

Zermatt > Montreux - 2 Nights (Lausanne is a large city and requires the subway to navigate because it’s on a steep hill. Montreux or Vevey are smaller and still have great access to the area)

Alternatively you could further narrow down to 3 stops by skipping Zermatt and doing Luzern 4 Nights, Wengen 4 Nights, Montreux 3 Nights

I'd skip Bern. It's not in the mountains. In your original itinerary, 2 nights in Luzern, with a day trip to Bern, would effectively mean no time in Luzern, which is much more interesting than Bern. Travel times are not insignificant.

Sorry, but I LOVE Bern, especially in the evenings, when work is done, and tourists gone.
SO many quaint alleyways and parts that are hundreds of years old.

September is a great time!
I think you need four nights in the Berner Oberland (Murren or Wengen). Don't you want to maximize time IN the Alps? No one is ever ready to leave. And I agree, eliminate nights in zurich. Add a day to Lucerne, if you can. Two nights is really I full day.
Secure lodging asap. Since Covid, folks are booking 8-9 months out.
Enjoy this beautiful area!

Thanks everyone, I REALLY appreciate your help & advice! I will start booking hotels now.

I like the idea of staying in only 3 places - Lucerne (4 nights), Wengen (4 nights) and Montreux (3 nights). Would that mean eliminiting Zermatt or that a possible day trip from one of those 3 places? Other than the Matterhorn, is Zermatt worth a visit?

Not in my opinion.

You can easily do a day trip to Zermatt from Montreux. I did this in June 2022 and had a great day.

From my trip report:

I took an early train (6:43) to see the Matterhorn. And did I see the
Matterhorn. 😊 I love the Swiss trains and did not consider the 2.5
hour ride to be too long, especially considering the gorgeous scenery
in this part of the country. And the train station is right in the
town center. I wasn’t really expecting to see the Matterhorn as I had
read it’s always in the clouds. I guess I lucked out as I had perfect
blue skies. My first glimpse was just the peak over the buildings. So,
I kept walking and walking until I was out of the town center and had
perfect views. I have so many great pictures of the Matterhorn, pine
trees, and wildflowers. After about 100 pictures or so, I had a great
walk back towards the train station to find the Gornergrat station. A
great train ride up and there was even more of the Matterhorn. Still
blue skies with a few white wispy clouds. Made for some great
pictures. I would have loved to spend more time here, so it’s on my
list for a future trip.

https://community.ricksteves.com/travel-forum/trip-reports/solo-in-switzerland-my-trip-report

I enjoyed Zermatt so much I am going back for 3 nights this June.

Thank you everyone! Our itinerary is set as far as where we will be staying. Now just need to figure out excursions and sights to see.