Comment 3 for bug 1773810

I believe I've been running into this same bug as well. I've had it with Ubuntu 18.04 and now 20.04 both running as a VM under VirtualBox on Windows 20.

I've been able to configure the settings such that the screen will stay on seemingly indefinitely once logged in.

The issue occurs at the login greeter screen. I've tried changing the settings mentioned above for both the logged in user account and for the gdm user. I've also tried to configure them via /usr/share/gdm/greeter.dconf-defaults

Nothing makes any difference at the login screen. After ~20 minutes the VM's screen goes black and at that point will not come back it just stays black. I am still able to SSH into the VM (which is how I often make use of the vm, though I often do need to access it's GUI.)

If anyone has any idea what could be causing the login screen to blank, I'd really appreciate it. I end up having to restart the VM whenever this happens.