The version number is not a real software release. It is a technical constraint set by Apple's installers for older versions of iTunes (like 12.8.3) to prevent them from being installed on incompatible operating systems.

Apple officially discontinued iTunes for Mac with the release of macOS Catalina (10.15) in 2019.

If your Mac is running macOS 10.15 or later, you do not need to download iTunes. Its features have been split into several dedicated apps already installed on your system: iTunes - Apple Support Community