I have experienced the same issue when trying to record audio with Microsoft Powerpoint 2011 on macOS 10.14. Powerpoint does not show up in the list of app with access to the microphone (System Preferences -> Privacy -> Microphone).
Note that you can reset this list from the command line (i.e. the Terminal) using:
tccutil reset Microphone
This may or may not help you. In my case it didn't.
What did help, was to launch Powerpoint from the command line through iTerm (though I suspect, using the
Terminal.app works just as well). So on the command line, I've typed:
/Applications/Microsoft\ Office\ 2011/Microsoft\ PowerPoint.app/Contents/MacOS/Microsoft\ PowerPoint
I.e., I executed the executable in Powerpoint's
/Contents/MacOS subfolder. By convention, every application has an executable, meaning, you can launch every application that way (but the name of the executable will usually be different).
Launched this way, when I tried to access the microphone, the System asked me whether I wanted to grant
iTerm access to me microphone. After granting access, I was able to record audio through Powerpoint.
Obviously, this is just a hack to get things going. But sometimes a hack is all you need.