I am currently running a headless pi 4b and I am using mosh and VNC viewer to control it. I have specified in my config.txt file to boot into 1080p @60Hz however this only works if I have my 1080p monitor plugged in. Before if I would start the Pi without a monitor plugged in I couldn't use VNC viewer but now I can, it's just in the wrong resolution. It is currently outputting 1024x768 @ 60.00Hz, progressive instead of 1920x1080.
Below are the config settings I have changed along with disabling overscan. According to the RPi website group, 2 and mode, 82 should be outputting 1920x1080 progressive @60Hz. I got this information from https://www.raspberrypi.org/documentati ... t/video.md
# uncomment if hdmi display is not detected and composite is being output
# uncomment to force a specific HDMI mode (this will force VGA)