how to get macos to stop using external monitor
how to get macos, Mojave to stop using external monitor(HDMI). Turning monitor power off doesn't work.
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Like an external DisplayPort connected display, that HDMI connected monitor, even when powered off, will show that it is online in System Information : Graphics/Displays. The Arrangement tab in System Preferences : Displays will however, not be present.
It would not surprise me that a small amount of current is maintained between the powered off external display, and the Mac so that when the external display is again powered on, the Mac can detect the power event, and let the operating system do its thing recognizing the external display. If you don't want this, then unplug the HDMI cable.