macOS Mojave and Catalina apply strict rules on software installation. As a result, Store Visualizer installers of version 20.0 will generate a 'malicious software' message and fail to install. Fortunately, there is a workaround.
When double clicking the installer, you will get this message:
"Store Visualizer.pkg" can't be opened
because Apple cannot check it for malicious
For versions higher than 20.0, we will make sure that our installers are trusted by Apple.
For version 20.0, please follow the workaround.
Click OK on the 'malicious software' message.
Go to System Preferences > Security & Privacy > General. You will see the following dialog:
In the Allow apps downloaded from section, make sure that App Store and identified developers is selected. A message stating that the package is not from an identified developer appears with an Open Anyway button.
Click Open Anyway.
In some OS versions, the installation will start right away. Otherwise it will show you the same 'malicious software' message, but now with a grayed out Open button:
Click the grayed out Open button and you will be able to install the software.