Itinerary help ( 7 days ) first time visit Switzerland Early May

I’m confused by some of your itinerary. You say Montreux 2 nights but then only show 1 night. Do you have 7 full days + arrival/departure days or do the 7 days include arrival/departure (5 full day). Do this entire thing by train, don’t rent a car. And if you only have 5 days, I’d recommend only 2 bases instead of 3 (Montreux + Zermatt OR Montreux + Wengen or Grindelwald OR Zermatt + Wengen or Grindelwald) - If you have 7 full days, something like this…

Day 1 - Geneva > Montreux -explore town
Day 2 - Walk the lake promenade to Chateau de Chillon, Return by Boat (evening Train to Zermatt?)
Day 3 - Zermatt - Gornergrat
Day 4 - Zermatt > Wengen or Grindelwald
Day 5 - Wengen or Grindelwald - Jungfraujoch
Day 6 - Wengen or Grindelwald - First, Lauterbrunnen or Murren/Gimmelwald/Schilthorn

Day 7 - Wengen or Grindelwald - Lake Brienz Boat tour
Day 8? Wengen or Grindelwald to Zurich for departure?

I can have 7 full days and I do not rent a car, it will be all by train. The schedule you suggested, which is the golden pass train?
Also I should buy a 7 day swiss travel pass right?

If you want a scenic train from Zermatt to Interlaken, go to Brig, then to Spiez via Kandersteg. This way takes longer, but avoids the Loetschberg Base Tunnel, which is 20 minutes completely under the mountains. The route via Kandersteg has a shorter tunnel and goes mostly over the mountains.

You can get to Brienz either by boat or train. Then Brienz to Luzern, which is a scenic section of the Golden Pass Route. Then Luzern to Zurich airport.

I am still planning my trip, I can do 8 days. One question is: is early May a good time to visit Zermatt? I really want to see Matterhorn, but heard weather is unpredictable.
Should I consider skip Zermatt? Just do Interlacken and Mount Jungfrau?