From your Windows computer, please open your Microphone privacy settings and make sure you allowed apps to access to your Microphone as shown below:
Be reassured, nothing is recorded from your computer mic, but Guitar Pro 7.5 needs to access it for two features available in the program: the polyphonic tuner and the Line In option.
If your issue is not fixed.
Access the Guitar Pro 7 Preferences from the:
File > Preferences > Audio/MIDI menu
Switch the Audio Input to None
If your issue is not fixed we invite you to follow this article