Add an App and give it permissions to access Downloads in Catalina

How do I give an app permission to access Downloads in Catalina?

The app does not appear in the list of apps. I unlocked the settings which you can see in the screenshot below but the + button is still grayed out so I can't add an app.

The app in particular is Screenflow and in trying to drag and drop an .mp4 file from Downloads into it. When I do I get this error which I'm only guessing is related to permissions

The error message was "Error Domain=NSPOSIXErrorDomain Code=-1 "Unknown error: -1" UserInfo={NSLocalizedDescription=Connection interrupted}"

I have the same issue with Octave 3.8.0's GUI version. No OS level error gets displayed but the app cannot access Downloads and no way to add in the Security and Privacy System Preferences Privacy Tab

>> QKqueueFileSystemWatcherEngine::addPaths: open: Operation not permitted
Warning: QFileSystemWatcher: failed to add paths: /Users/gregg/Downloads

>> cd Downloads
warning: load_path: .: Operation not permitted
error: cd: unable to find current directory
error: cd: unable to find current directory
>>

Note: There are newer versions of Octave for MacOS but Stanford University machine learning courses require version 3.X

I have the same error and I find the reason here.

The reason is your Octave 3.8.0 is too old for your OS Catalina, you should download a new version of Octave(4.4.1 or 5.1.0). You can download the new version: https://wiki.octave.org/Octave_for_macOS.