x11vnc server with no monitor

sudo apt install xserver-xorg-video-dummy

/etc/default/grub
GRUB_CMDLINE_LINUX_DEFAULT="nomodeset"
sudo update-grub2

/usr/share/X11/xorg.conf.d/xorg.conf
create xorg.conf

Section "Device"
    Identifier  "Configured Video Device"
    Driver      "dummy"
    VideoRam 256000
EndSection

Section "Monitor"
    Identifier  "Configured Monitor"
    HorizSync 5.0 - 1000.0
    VertRefresh 5.0 - 200.0
    ModeLine "1920x1080" 148.50 1920 2448 2492 2640 1080 1084 1089 1125 +Hsync +Vsync
EndSection

Section "Screen"
    Identifier  "Default Screen"
    Monitor     "Configured Monitor"
    Device      "Configured Video Device"
    DefaultDepth 24
    SubSection "Display"
    Depth 24
    Modes "1920x1080"
    EndSubSection
EndSection