macOS Mojave introduced a new security framework for handling input devices such as microphone and camera.
In order to use microphone or camera applications now have to prompt the user for access (in similar way as is seen on iPhone).
The permissions that are currently active in the new security framework can be seen in “System Preferences” -> “Security and Privacy” -> “Privacy” tab. Camera and Microphone are now listed in Mojave which was not the case in macOS High Sierra. The TeamTalk application has to be added to the exception list here in order to be able to transmit voice and video.
Users have reported the problem in this Issue on GitHub and a beta version, v5.3.5, now addresses this issue. Please try it out.
Note that there’s also a new installer for the TeamTalk application (it’s a .pkg file now instead of a .dmg).