Do the regional trains also run over Landwasser Viaduct,

The regional trains run on the same tracks as the panoramic trains. Heading south on the Bernina Express route, I'd say sit on the right side of the train, but you'll still be jumping across the aisle for the sights. It's a fantastic ride!

Sit on the right side toward the back of the train. Then you will see the train in front you on viaduct as the tracks curve just before entering the tunnel. I took a great photo of that, right through the window.

Lola, that's a great point! I also have those pix.

same stations, same track, same views, better windows. The Landwasser viaduct with open windows followed by the tunnel is an excellent reason for a local train. The windows don't open on the named trains unless you are in one the plain cars added on.

I think the Brunio Spiral Viaduct is more impressive. It's south of the Bernina pass followed by some interesting street running
You can check out the view from the train on Google Street View. One of the few railway journeys where this is possible

Thanks Mission accomplished today; I looked for it but did not notice when the train was on the Brunio after passing Miralago.

You can see the spiral viaduct on the Swiss rail map here:

https://cdn-doc.myswissalps.com/docs/default-source/rail-network-maps/swisstravelpass.pdf?sfvrsn=7788603a_56

And a photo here:

https://www.amusingplanet.com/2013/10/brusio-spiral-viaduct-in-switzerland.html

It is an impressive engineering feat, and very interesting, but when you are on it, I don’t think it is as visually stunning as the Landwasser one which is higher in the mountains, and much higher off the ground.

A medley of photos here (note that the 3d one in the top row is not the Landwasser viaduct):

https://www.shutterstock.com/search/landwasser+viaduct