My config: Mid 2012 Mac mini connected to a projector via HDMI. The projector is typically off and the Mac mostly works headless.
This setup has worked for me for a couple of years now. Ever since I upgraded to Sierra (10.12.3), I get only a black screen with the mouse pointer being visible though. When I log out (cmd+shift+q), I sometimes get an image but it does not really update and is displaced.
Once I turn the projector on, screen sharing will also start working – even if I turn the projector off again. SSH always works without issues.
Any clues how I can fix that?
What I tried (will update):
- SMC reset
- NVRAM reset
- killing the Screen sharing service
- Running "First aid" in disk utility (also from the Rescue partition)
- Run maintenance scripts in Onyx
Update 1: This seems to be a related Apple Discussions thread.
Update 2: I added an answer that gives some hints. Can anyone help me find a better solution, please? My guess is the GPU has to be force enabled somehow, e.g. in bash...