Apple has included iTunes 188.8.131.52 with the macOS 10.14.5 update. The previous version of iTunes was 184.108.40.206. The new version is only available when the operating system is updated and there is no stand-alone installer.
There doesn’t appear to be too much different. However, as in iOS 12.3, there are some minor changes to Apple Music’s For You page. For example, the 4×4 “because you like/listen” blocks of album recommendations have been replaced with 4 Genre groups of 12 albums and playlists. [Update: this was rolled out to all users.]
This is probably the last version of iTunes that Apple releases before the macOS 10.15 beta is released to developers in June at WWDC; it is presumed that a new Music.app will debut then as well.