The problem is that the Linux kernel is telling us there are two displays:
LVDS - a laptop display that does not exist
VGA - your real monitor
And then due to bug 1760849, gdm3 is putting the login screen on that laptop display which doesn't really exist.
A fix for bug 1760849 would suffice. But let's keep this bug open and make this bug just about the kernel bug of reporting an LVDS output which doesn't exist.
Great! I think I understand the problem now.
The problem is that the Linux kernel is telling us there are two displays:
LVDS - a laptop display that does not exist
VGA - your real monitor
And then due to bug 1760849, gdm3 is putting the login screen on that laptop display which doesn't really exist.
A fix for bug 1760849 would suffice. But let's keep this bug open and make this bug just about the kernel bug of reporting an LVDS output which doesn't exist.