This is definitely software / firmware related from what I can see.
GPD have properly messed something up with the power management settings in Bios 0.23
My screen goes black after I walk away for 10 minutes in Ubuntu Mate 19.10 or in Windows.
This is the setting which is set to save battery. Only you cant get the screen to wake or come back on.
The only thing I can do is change the backlight of the screen from low to high.
I know the system is still functioning as when I press the power button I can hear the Ubuntu Mate sound pop but screen is black.
This is the most annoying problem I have ever come across.
I should not have to belly button the machine everytime I pause to get a coffee.
Short term fix or workaround is dont allow your screen to go off in power management settings.
But I should not have to do this.