If you have an AMD Ryzen CPU paired with nVidia GPU you will run into some problems as Ubuntu does not play well with this pairing. In order to remedy this you have to tweak configs a bit by yourself.

Cause of the problem: Ubuntu’s prime-select feature still does not work for AMD/nVidia pairing and requires manual tweaking, it works only for Intel/nVidia pairing.

Modify /etc/X11/xorg.conf if exists, or create if it does not

sudo nano /etc/X11/xorg.conf

Inside paste the following

Section "ServerLayout"
  Identifier "layout"
  Option "AllowNVIDIAGPUScreens"
EndSection

Modify /usr/share/X11/xorg.conf.d/10-amdgpu.conf

sudo nano /usr/share/X11/xorg.conf.d/10-amdgpu.conf 

replace

Driver "amdgpu"

with

Driver "modesetting"

Modify OutputClass of /usr/share/X11/xorg.conf.d/10-nvidia.conf

sudo nano /usr/share/X11/xorg.conf.d/10-nvidia.conf 

by adding

Option "PrimaryGPU" "Yes"

Caution! This step needs to be repeated after every nVidia driver update.

Create two files named optimus.desktop in the following locations

• /etc/xdg/autostart/
• /usr/share/gdm/greeter/autostart/

sudo nano /etc/xdg/autostart/optimus.desktop
sudo nano /usr/share/gdm/greeter/autostart/optimus.desktop

Inside both paste the following

[Desktop Entry]
Type=Application
Name=Optimus
Exec=sh -c "xrandr --setprovideroutputsource modesetting NVIDIA-0; xrandr --auto"
NoDisplay=true
X-GNOME-Autostart-Phase=DisplayServer

Caution! Exec… line is long, make sure it is actually one line

After all files have been modified correctly – reboot

Greeter displayed on the wrong screen

Caution! If you have the auxiliary display plugged in, greeter might be displayed only on the auxiliary monitor! Mouse movement can be restricted to that monitor as well!

• Open Ubuntu Settings
• Navigate to Displays
• Select Single Display option
• Set Primary Display to 1 Built-in display
• Click Apply
  • You should have only your laptop display working right now
• Go back to Displays settings and set them however you like now
  • Displays should work correctly now
• To force greeter on built-in display open terminal and run the following

cd ~/.config
sudo cp monitors.xml /var/lib/gdm3/.config/

Now everything should be set-up correctly

Source: https://forums.developer.nvidia.com/t/nvidia-xconfig-doesnt-do-what-i-want-it-to-nor-does-nvidia-settings/107883/7