The solution is to allow TntConnect to "control your computer" in the Security & Privacy settings.
Checked the box to allow TntConnect to "control your computer":
Also, in the "Automation" section, TntConnect should be able to control "System Events".
Now TntConnect should be able to "Search for a Database..."
If you still can't use the "Search for a Database..." feature on your Mac
1. Open Finder.
2. Under the "File" menu, click on "Find" (or click Cmd+F).
3. Type in mpddb.