RTX 3060 laptop + Ubuntu 20.04: unable to detect internal monitor

Problem solved by installing Intel driver.

Both monitors are working now

$ inxi -G
Graphics:
  Device-1: Intel driver: i915 v: kernel 
  Device-2: NVIDIA driver: nvidia v: 470.86 
  Display: x11 server: X.Org 1.20.13 driver: modesetting,nvidia 
  resolution: 1920x1080~60Hz, 1920x1080~144Hz 
  OpenGL: renderer: NVIDIA GeForce RTX 3060 Laptop GPU/PCIe/SSE2 
  v: 4.6.0 NVIDIA 470.86 

$ xrandr --listproviders
Providers: number : 2
Provider 0: id: 0x1b8 cap: 0x1, Source Output crtcs: 4 outputs: 6 associated providers: 1 name:NVIDIA-0
Provider 1: id: 0x200 cap: 0x6, Sink Output, Source Offload crtcs: 4 outputs: 3 associated providers: 1 name:modesetting