short cut keys to display on external monitor
short cut keys to display on external monitor from macbook 12 inch
MacBook
In addition to info linked in support article cited above, there are essential details in following as well.
• Get help with video issues on external displays connected to your Mac - Apple Support
https://support.apple.com/en-us/HT201177
There are just too many variables and unknowns, so you will have to learn how to use instructions.
Good luck & happy trails!
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