EDIT: An underlying issue resulting from launching Wwise with a project directly from the Launcher causes the Audio Input to crash Wwise on macOS. Until this issue is resolved, the workaround is to launch Wwise directly from the Wwise tab in the Launcher or from Finder by double-clicking on Wwise.app.
The privacy settings for Microphone must be requested by the application. I can confirm this behavior works as intended in 2019.1.11, which is the version used for the 301 course.
If you are on a multi-account machine, make sure the permission is not granted on another user's account and that your user account has the permission to modify the privacy settings.
You can try resetting the microphone permissions globally by running the following command in Terminal.app:
tccutil reset Microphone
The applications list in the Privacy panel for the Microphone permission should be empty following that command. Try reopening Wwise and adding the Audio Input plug-in again: the popup should prompt you to allow the Microphone.
If this is still not working, you can try to reset the permissions of the other accounts on your machine.