How to fix that app can't open on macOS Catalina?

After upgrading to macOS Catalina, some mac users feedback that MusicPlus "can't be opened because Apple cannot check it for malicious software". A dialog box pops up, click "OK" button and the application will close

Getting started with MusicPlus

Basic guidelines for new users

MusicPlus FAQ - Frequently Asked Questions

Answer the most basic questions about MusicPlus