I just tried it on Catalina to see how it looked and noticed there is no way to share the music library in Catalina at least the way I was doing it in iTunes (was using the "computer icon" on the apple TV to access the shared library from Mojave)
Maybe this has been moved somewhere else in the preferences - but I could not find it - so it seems that sharing is a missing feature?
I believe this has now moved to System Preferences:
https://kirkville.com/how-home-sharing-works-in-macos-catalina/