Comment 141 for bug 1871721

I am seeing the same problem on a Dell Precision 7750.

Ubuntu 20.04LTS
kernel: 5.11.0-27-generic #29~20.04.1-Ubuntu SMP

graphics: VGA compatible controller: NVIDIA Corporation TU106GLM [Quadro RTX 3000 Mobile / Max-Q] (rev a1)
plus Intel i915
processor: Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz

With nvidia-prime installed, running nvidia-settings presents three options:
NVIDIA (Performance Mode), NVIDIA On-Demand, Power Save
In Performance Mode, only the external HDMI port is active. Booting with no external monitor produces a blank laptop LCD display, but the external monitor is active. Using System Settings / Display, only the external monitor is detected. The keyboard secondary function key Fn F8 has no effect. Laptop screen is blank if booted without an external monitor connected.

In On-Demand mode, only the laptop display is active and the external monitor has no output. System Settings / Display detects both monitors. The Fn F8 key pops up a display mode selection tool to select how the screens will be configured, if the external-monitor-only mode is selected, the laptop screen is blank, and there is no display on the external monitor. All other selections have no effect.

In Power Save mode, only the laptop display is active and the external monitor has no output. System Settings / Display detects only the laptop monitor. The keyboard secondary function key Fn F8 has no effect.