4 minutes to change trains at Brig!

Not a problem- travel light. You need to be able to handle your luggage up/ down stairs. Be ready to jump off the train as soon as the train door opens. Know your platform numbers.
You'll get the hang of it quickly!

Platform 1 to Platform ? Which? If you are heading to Zermatt you will be using the outside tracks, Platforms 11-14, which will be a sprint. Here is a station map:

https://www.sbb.ch/content/dam/infrastruktur/trafimage/bahnhofplaene/plan-brig-a4.pdf.sbbdownload.pdf

If it is all on platform 1, then you get off one train, it departs, and another train arrives at platform 1 a few minutes later and you get on
As easy as it gets.

If going to Zermatt, no way this would be a legal connection.

4 minutes to change trains at Brig! Has anyone done this? Platform 1 -
Platform with luggage.

isn't this terrific? The Swiss Railways plan their trains so, that you do not have to waste time hanging around a station. They make sure to keep you moving, as they know that people prefer being on trains, rather than on a platform.

The Swiss railways transport more than 1 million passengers a day. A lot of those make connections like this, so yes, lots of people do that every day. And in the unlikely case you miss your connection you just take the next train.

4 minutes is a legal connection at Brig. It often turns up if you want to travel from Milano to the Bernese Oberland (which I believe the OP wants). You board an EC in the direction to Geneva, and in Brig change for an IC direction Basel. The change is cross platform normally, and the IC will even wait a few minutes if needed. If the EC from Milan has a non trivial delay the IC will not wait, but there is another northbound IC half an hour later, so you just take that.

Platform 1 -- to Platform 4. With luggage.

You will have to use the stairway or the ramp. Walk about 100 ft in 4 minutes.

Be standing in the carriage vestibule with your luggage as the train pulls into Brig station so you can get off the train quickly. Coming from Italy, Brig will be right after you emerge from the long Simplon Tunnel.

Wow, you guys, thank you so much!

And an especial thank you to Sam. :)

What date and time is this? Because if his is what I think it is, it is going to be 3 to 4.

The OP has been using Eurail for the schedules and platform numbers, and recently said things have changed, from 4 minutes to transfer, to 34 minutes. Do we even know when this trip is?

https://community.ricksteves.com/travel-forum/switzerland/eurail-posted-train-times-vs-db-navigator

I saw an itinerary from Milan on the EC train to Sion. Connection at Brig is from Track 1 to Track 4 to go to Spiez, with a 4 minute transfer time.

Yes. Currently the EC trains direction Geneva only go as far as Sion, where you are transferred to a bus (because of trackwork).

he 4 minute transfer in Brig is a timed transfer. That means that if, for example, the EC is 3 minutes late then the IC is going to leave 3 minutes later as well. The staf on trains and at stations keep an eye out for transferring passengers, to make sure everyone makes their connection.