The issues on Catalina are NOT driver related, but related to some of the new security and permissions requirements in Catalina.
First, when an application attempts to access any sound input device, said application requires explicit permission from the user before it can access the mic. Second, there are additional protected folders in Catalina that applications also need to explicitly ask permission to access (such as Desktop and Downloads). For some reason, Audacity does not ask for these permissions, and as such can’t access the necessary resources to work.
However, there is a work around!
You can open Audacity via the terminal using the following command:
open /Applications/Audacity.app/Contents/MacOS/Audacity
This will open Audacity and then Terminal will actually ask for the correct permissions. If for some reason this doesn’t work, you can try opening Audacity as root:
sudo open /Applications/Audacity.app/Contents/MacOS/Audacity
Finally, this assume that Audacity is stored in your Applications folder. If it’s somewhere else, you’ll need to change the path in the above command:
open /location of audacity/Audacity.app/Contents/MacOS/Audacity
For example:
open /Applications/Utilities/Audacity.app/Contents/MacOS/Audacity
Hopefully these issues can be solved in short order (I haven’t run into anything similar with other apps).