This happens on all distros and all desktops environments.
It is something that distro developers could never imagine of !!!
When I boot, live LXQT (other environments too) on notebook with broken self monitor
and single extended monitor,
the linux system thinks that both monitors are active. (actually not)
And displays extended destop on extended monitor.
There is nothing on that screen other than background color and mouse cursor.
Start button and other dekstop short cuts remain on main monitor. (which is not functional)
I need display configuration or at least a terminal.
Alas!! Non is available !
Neither on mouse right-click.
I need one of those under mouse right-click
mate: mate-display-properties
KDE: kscreen
LXQT: lxqt-config-monitor
LXDE: lxrandr
ALL other: arandr
Terminal: xrandr
It would be complicated to to configure all destop evironments.
Easiest way to do is to miror all displays on live CDs with auto-run xrandr command.
And place screen configuration shortcut on all desktops. (mentioned in earlier post)
This script is this (in go language)
https://github.com/pocke/xrandr-mirror
I hope this is will be included in future Sparky releases...