I was debating whether this was a calames issue or a distro one but since there maybe ways this can be handled in the caller, I’ll try here first.
If a second screen is attached ( eg VGA monitor attached to a laptop ) calamares apparently assumes the user wants dual monitor setup and splits the desktop over two screens.
There is another possibility which seems to have been missed here : defective laptop screen. Since backlight failing ( or shock damage ) are relative recurrent failings this is probably not such an unusual situation for an older laptop which someone may want to install a light Linux OS on.
Under dual monitor mode, the LH side of the desktop with the icons and the system menu is on the internal display. The empty RH half is relatively useless. Worse, the installer fires up on the internal screen : leaving the user blind in the case of a broken backlight. It appears that the installer has failed to start.
A safer assumption may be that if an external screen is attached, the user wishes to use it. So this would be a safer place to direct single monitor output of the installer, irrespective of why there is a second monitor present.
Ultimately, on firing up the live ISO image, it may be safer to go mono desktop on the external VGA and provide an simply means to flip to dual if that is desired. This should provide a safe route to cover all bases.
In the meantime , is there a way to hack the desktop icon or run it from a terminal with arguments to force it to display installer output on the external VGA. I have a real case of broken screen laptop I wish to install lubuntu on.
Thanks for any workarounds.