After I updated to Mojave, I can no longer use the automator service I\'ve previously been using with the alert below.
I was still having issues sending keystrokes a few months after Mojave was released. For me, weirdly the fix was to go System Preferences -> Security and Privacy -> Privacy Tab -> Unlock the Lock with your password -> Remove (with the minus button) Automator from the list of Apps in the Accessibility Row. Maybe there was something from running the betas that needed to get deleted before my scripts could send keystrokes again.
Edit: After quitting System Preferences I was getting the alert error again. Re-adding Automator.app to the Accessibility row seems to have fixed this for now.