Howdy!
We have a post on how to resolve this issue Here.
In summary:
- Press Control + M to switch to Windowed mode.
- Go to System Preferences > Security & Privacy > Privacy > Accessibility. If Heroes of the Storm is listed here, make sure it is checked. If the game is not listed here, you can proc the permissions prompt by checking the Disable OS Keyboard Shortcuts option in the Mouse & Keyboard settings of the game.
Thank you!