Most presentation programs write pixel information directly to the monitor. Because of the way video mirroring works, you have to make the external monitor the main monitor. This is done in the Monitors control panel.
Setting External Monitor To Main Monitor
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1) Open Monitors control panel
2) Set external monitor to main monitor by dragging the miniature menu
menu bar to the image of the external monitor.
Note: You have to change the monitor before you turn on video mirroring.
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