Mojave has expanded macOS's sandboxing rules for files and devices. When an application needs to use the camera or microphone, the user is supposed to get a prompt the first time to authorize it. Unfortunately, since updating my MacBook Pro to Mojave, none of my applications issue this prompt, and they can no longer use the camera nor microphone. I have found two exceptions: FaceTime and Safari +
appear.in. No other browsers (Chrome, Firefox, Opera) nor video-conference services (Google Hangouts, Google Talk, zoom.us, Skype) work.
According to Apple's documentation, permissions can be reset on the command line using
tccutil reset Camera and
tccutil reset Microphone. These commands run without error for me, but there is no change to behavior. No prompts are ever issued from the system for any of these attempted interactions.
I have also observed multi-application interactions that no longer work. For example, the Last.fm Scrobbler is supposed to interface with iTunes to log the music being played, but this feature is now broken on my system.
In the Security & Privacy dialog in the Privacy tab, the Camera and Microphone panes are empty ("Apps that have requested access to your camera/microphone will appear here."). And the Automation pane has only a couple of items, no Last.fm or iTunes. And unlike the Accessibility pane, these panes do not have +/- buttons to manually add entries.
My question is: how can I troubleshoot this further?
Edit: It occurred to me to try disabling mySIMBL, a macOS plugin manager that purports to require System Integrity Protection (SIP) and Apple Mobile File Integrity (AMFI) both be disabled. I clicked the "Uninstall SIMBL" button in the mySIMBL preferences System Info pane, and reenabled AMFI, then rebooted. Afterward, the system started successfully prompting me for permission for camera, microphone and inter-app communication.
While I am glad to have fixed my problem, the question of how to troubleshoot macOS's Security & Privacy—how to dig deeper and understand in more detail what is happening—is still valid and unanswered here. So I will leave the question open.