In September, we will be flying into Zurich, spending 4 nights in Switzerland at Bern and Bettmeralp, then making our way south into Italy. Just now I was doing some advance planning on our strategy for Switzerland (HFC and/or Saver Day Passes or tickets), looking at each travel day and the costs.
I found that for Bettmeralp to Milan, which would normally be a simple journey via Brig and Domodossola, possibly with no changes between Brig and Milan, that route was not shown at all, no matter whether I checked for June, July, August, or early September. The options were (1) eastbound from Betten on the Glacier Express tracks to Andermatt, change to Göschenen , and south via the Gottardo route to Milan, likely with a change at Lugano or elsewhere, (2), from Brig to Zurich to catch a train over the Gotthard Pass route to Milan, again with one or more changes on the way, (3) Brig to Domodossola, changing there to the Centovalli slow train to Locarno, and then to Milan, and (4) other more complicated options involving buses.
Obviously, there is going to be a problem on the route between Domodossola and Milano, and found this webpage with the explanation: the tracks will be completely closed between Arona and Stresa from June 9 to September 8.
https://showmethejourney.com/travel-news/a-summary-of-major-construction-projects/
The website shows planned construction works for every country, so it is worth checking if you will be in Europe this summer. And maybe someone can post other websites with more detailed or up-tp-date information.
Fortunately for us, our actual travel date to Italy is September 21, so the work should be done by then, and we can take the normal route. At least I hope so. I should be able to find out later, like July, when I look at the routes and costs again.
And if not, I guess I can look at this as an opportunity to ride my favorite Treno Gottardo again, or try out the Centovalli scenic railway. But it would mean spending another night in Switzerland, and taking one away from Italy (specifically Modena, which is our first stop).