When I try to open the default synthesizer on macOS 14.1, I get a dialog saying that <application> requests access to the device's microphone.

This is actually tricky to test. I ran the test program from Terminal and got this dialog. But now I can run it from Terminal and I do not get the dialog, even after turning off microphone permission for Terminal in System settings and restarting Terminal.

I got similar results running the program under IDEA.

By debugging the program, it seems that the SourceDataLine that is opened is the Default Audio Device. I don't know how the Default Audio Device is defined (it does not seem to matter which input device I select in Settings), but apparently it provides access to the microphone. This is inappropriate for an application like the synthesizer which only outputs sound.