- I have upgraded to Parallels Desktop 12 for Mac, and now my virtual machine's display image is black on external monitor in Full Screen.
Parallels Desktop 12 for Mac supports only native macOS Full Screen mode. After the upgrade to Parallels Desktop 12 your virtual machine is now using the native macOS full screen mode.
Any other application on a Mac will behave the same way: after entering full screen with the external monitor attached, the image on external display will be black. This is the native macOS behavior, see the below discussions for more details:
- Dual monitors and fullscreen fiasco, is there a work around?
- Why does Mac OS X turn off monitor #2 when an application is maximized on monitor #1?
- Go to > System Preferences > Mission Control.
Enable Displays have separate Spaces option.
- Log out from Mac user account and log in back.
Enter Full Screen view mode with your virtual machine. To extend virtual machine to the external display go to View menu of the virtual machine > Use All Displays in Full Screen