ralsina
When enabling a monitor, there is no physical size information
To reproduce:
- Start with a disabled monitor
- Enable it
- Try to set it to scale to physical size
It fails with an error, because when xrandr info was collected, the physical size information is missing.
In some cases (laptop monitors) we can get this via xrandr --verbose + EDID even if it's turned off.
Getting it via xrandr --verbose + EDID works for anything that is connected. If it's not, then it doesn't work (which makes sense)
Bear in mind that some monitors straight up tell lies about physical size. I've had one monitor that reported itself as a 7" diagonal for some reason.
Nowadays most monitors seem to be fairly honest, although there is already a case of a monitor reporting to be smaller than it really is. The "scale so windows are the same physical size across monitors" is a bit of a gimmick anyway ;-)