How to remote desktop into Ubuntu with no monitor?

In Ubuntu v22.04, and many other Linux GUI systems, the display output is disabled if there’s no monitor plugged in, so Remote Desktop (VNC, RDP, or xRDP) won’t start a desktop session. However, you can “fake” a monitor using a dummy HDMI/DisplayPort setup.

Run these commands:

sudo apt update
sudo apt install xserver-xorg-video-dummy
sudo nano /etc/X11/xorg.conf.d/10-dummy.conf

Add this to the .conf file

Section "Device"
    Identifier  "DummyDevice"
    Driver      "dummy"
    VideoRam    256000
EndSection

Section "Monitor"
    Identifier "DummyMonitor"
    HorizSync 28.0-80.0
    VertRefresh 48.0-75.0
EndSection

Section "Screen"
    Identifier "DummyScreen"
    Device     "DummyDevice"
    Monitor    "DummyMonitor"
    DefaultDepth 24
    SubSection "Display"
        Depth 24
        Modes "1920x1080"
    EndSubSection
EndSection

Then restart the display manager.

sudo systemctl restart gdm3 

Now try to remote desktop in again and it should work.