Is it worth it to get a rail pass for a day and a half in Switzerland ?

Where are you arriving from when you arrive in Zurich? This is a very compact and heavy schedule for 4 days. Doable. Hopefully the weather will cooperate with you in the Alps. What did you mean visit remaining sights in Switzerland? I wouldn't buy a train pass. Just individual tickets. No cars allowed in several places like Murren and Gimmelwald. Good travels.

Looking at your travel starting in Zurich you might go with the Swiss Travel Pass 4 days
https://www.sbb.ch/en/leisure-holidays/travel-in-switzerland/international-guests/swiss-travel-pass.html

You just have to add up the costs of all of your rail travel and mountain excursions to see if the costs exceed 270 CHF.

This looks like you have no time to visit the places you want to.

- Day 1: Arrive in Zurich in the morning. Take a train to Colmar. Rent a car in Colmar to visit the Alsace region.
Do you mean Zürich airport? I guess you are flying in from outside Europe. When do you land? By the time you have got through immigration, the train takes 2½ hours, then you need to pick up the car. It will be afternoon. You cannot "visit Alsace" in less than ½ a day. That is not even enough time to visit Colmar town.

- Day 2: Leave Colmar around afternoon time to take a train to Interlaken. Stay the night .... somewhere
Again, ½ day in Colmar

- Day 3: Go up the Schilthorn, visit Murren Grimmelwald, Lauterbrunnen valley
A very busy day.

- Day 4: Visit remaining sites in Switzerland, and then take a train to Lake Como Italy....
Visit the whole of Switzerland in ½ day?
Where on lake Como? From the Berner Oberland to most places on lake Como you need to go via Milan. Interlaken to (for example) Varenna takes 5 hours. The fastest train is 13:29 depart Interlaken Ost, 18:23 arrive Varenna.
If you need to be at Interlaken station at 13:29, you cannot go too far away that morning.

You need a lot more nights, or less places.

P.S. there is no such place as "Grimmelwald", you either mean Gimmelwald or Grindelwald.

I really think this whole concept is seriously misguided. You aren't giving yourself enough time anywhere, and you're going to spend a great deal of money in the process.

@threadwear I am coming from the U.S. I will arrive at 8:30 a.m. in Zurich. When I said remaining sights, I mean visiting the Oberhofen castle, and lake Brienz, after going up the Schilthorn, Murren, Lauterbrunnen valley…. DO you think it is possible? Or should I give 2 days in Switzerland to visit Schilthorn, Murren, Gimmelwald, Lauterbrunnen valley?

Thank you!

Hannah

@threadwear I am coming from the U.S. I will arrive at 8:30 a.m. in Zurich. When I said remaining sights, I mean visiting the Oberhofen castle, and lake Brienz, after going up the Schilthorn, Murren, Lauterbrunnen valley…. DO you think it is possible? Or should I give 2 days in Switzerland to visit Schilthorn, Murren, Gimmelwald, Lauterbrunnen valley?

Thank you!

Hannah

What will you do if your one day is that day that week that gets low clouds and fog for at least half the day. It is a long way to go to miss all that you went to see. Two days gives you a 100% better chance of doing what you want.