How do I undo "Command Q"?
My mouse will not reconnect to the desktop
iMac (Retina 5K, 27-inch, Late 2015), OS X El Capitan (10.11.6)
Command + Q is the shortcut to quit an app.
Mac keyboard shortcuts - Apple Support
It has nothing to do with your problem
Have you tried:
Apple Wireless Keyboard: Difficulty during pairing process - Apple Support
If your Apple wireless mouse, keyboard, or trackpad aren't working as expected - Apple Support