Pausing an emulator (VPX/FP/ZEN FX) is usually different for each emulator. So it must be configured differently for each.
Steps to confgure VPX pausing.
Download zip file if you don't have VPXPAUSE.EXE already. Place this file into the LAUNCH sub-folder of pinupsystem. Remember to UNBLOCK ZIP!
https://www.nailbuster.com/pup/VPXPause.zip
Step 1: In Popper Controller Setup set a key/button to 'In Game Script'. This key should not be something like ESC or Q that VPX defaults as its pause menu. You can also look at your controller and see if it supports 'SHIFT' button/key combos.
Step 2: In emulator setup VPX: In OTHER tab set it In Game Script to
START "" "[STARTDIR]Launch\VPXPAUSE.exe"
Tha'ts IT. Now when VPX is running this PAUSE message will appear on by BackGlass 'flashing'. Press the pause button again and it will close.
note: while running it will also check if vpx is actually running, it will close automatically if vpx is not running.