My Pi 4s would boot up just fine with a monitor connected and I could also VNC into them with no issues. However, with no monitor connected I at boot I could no longer VNC in, ssh still worked though. VNC did connect but showed a "No Screen to Display" error.
To force the video system to start with no monitor connected:
Change these lines to look like this: ( The 2 : 0x53 gives you a working 1600 x 900 option that works good on a 1980x1080 screen )
Code: Select all
# uncomment if hdmi display is not detected and composite is being output hdmi_force_hotplug=1 # uncomment to force a specific HDMI mode (this will force VGA) hdmi_group=2 hdmi_mode=0x53
Then set your preferred resolution with the screen tool and reboot.
HDMI Group and Modes list and much other good information: