Found this on another site and thought I would post here in the hopes it helps.... Your pi's GUI isn't starting on headless reboot because you don't have a default resolution set in raspi-config. Go to terminal edit raspi-config: sudo raspi-config Under "Advanced" settings you can set a default screen resolution and frequency so that your GUI will start without a monitor (by default it pulls these from the monitor). Teamviewer 14 worked for me without issue after doing this on Rasberrypi 4. Hope this helps someone else with my issue!!
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