send the notifications when it matters

lot easier

Let me fork that and see if I can make that work.

but it needs notifications

you can certainly detect the orientation in css

on another app i support

:root{
  --scale-factor: 1;  /* set default scaling in case we have partial window, debug or in vm terminal window */
  --design-width: 1920px;
  --design-height: 1080px;
}

@media screen and (orientation: landscape) {
    :root{
        --scale-factor: var(width) / var(--design-width);
     };
 }
 @media screen and (orientation: portrait) {
    :root{
        --scale-factor: var(width) / var(--design-height);
     };
 }

/*@media screen and (width:3840px)  and (orientation: landscape) {
    :root{
    --scale-factor: width/var(--design-width);

    };
}
@media  screen and (width:1080px)   {
    :root{
    --scale-factor: width/var(--design-width);
    };
}*/

It might be nice to have it up on the TV in another room or on a second monitor while I’m working. Those will be in landscape.

I think it can be done with shifting CSS mostly(https://forum.magicmirror.builders/topic/13197/change-the-regions-positions). But modules that use full screen might be a challenge.

while the exact location and size changes by device orientation
the logical placement is the same

you could create another config.js or make those variables
and use the envsub/template support to change the variable definitions in the script that starts MagicMirror

using older xrandr

#!/bin/bash

orientation=$(xrandr | grep " connected" | awk '{print $2 " " $3 " " $4}')

if [[ $orientation == *"left"* ]]; then
  echo "Screen orientation: left"
elif [[ $orientation == *"right"* ]]; then
  echo "Screen orientation: right"
elif [[ $orientation == *"inverted"* ]]; then
  echo "Screen orientation: inverted"
else
  echo "Screen orientation: normal"
fi

see https://docs.magicmirror.builders/configuration/introduction.html#configuration-template-system