I’ve also tried installing just a clean raspbian stretch. However, the problem persists when I rotate the display with only the desktop environment of stretch running. I’m now thinking that the 32" Samsung I’m using may be the issue and I’m going to try out another make/model.

Here’s an update with an even better fix! While beginning my journey into custom css, I quickly came across another fix to the poor graphics of a vertically rotated screen. In my opinion, this fix is even better than using xrandr because this fix saves a ton on performance, results in a look just as good as using the screen in its native horizontal look, and once you implement it, it will stay implemented. All you have to do is copy and paste the following to your MagicMirror’s custom css: body { margin: 0; position: absolute; transform: rotate(90deg); transform-origin: bottom left; width: 100vh; height: 100vw; object-fit: cover; top: -100vw; visibility: visible; } There you go, just like that you’re set. The custom css of modules may have to be edited as well to make it work but that’s a small price to pay for a much better finished product. Credit where credit is due, I found this fix right here on the forum!