Just doing some testing for a project. The project involves two SBCs right now(one is the Raspberry Pi 4b). I have one TV handy so I had the other SBC connected initially. For reasons pertaining to the project, I turned on both SBC's simultaneously. The Pi started unplugged to any HDMI port.
Later I prompted a proper shutdown on the connected SBC and then connected the Raspberry Pi's HDMI to the TV. I intended to initiate a shutdown on the Pi as well. However, I could not get the image to appear. Only stating "no signal". I tried other HDMI ports on the TV, the other microHDMI port on the PI, I borrowed someone else's TV and tried it...same problem. Curiously, when I remove the cord the TV displays "check signal cable", and when I plugged back in I get "no signal". Also I clicked my mouse/keyboard just to make sure the Pi wasn't in some "screen saver"/"sleep mode" as they do when you leave them idling temporarily.
Knowing no other way I unplugged the Pi to shut it down despite knowing that's risky. When I turned the Pi back on, the desktop page displayed normally.
I continued testing and forgot my earlier mistake. Turned off SBC 1, connected the HDMI to the Pi and same problem. I was forced to shutdown the Pi improperly a second time.
This leads me to my questions about the Pi:
When starting up, if the Pi does not sense a HDMI connection does it change a setting or something? Thus making a connection later not work?
If this happens again, is there a way to turn the Pi off correctly without a display?
Thanks everyone