While Apple Music does not automatically generate an library XML file, this can be done manually in the app itself.
While the old XML file is not automatically generated anymore, you can manually export an XML file of your Music library in macOS Catalina which — I will assume — is in the same exact format as the old iTunes XML file by following these steps.
First, open up the Music app, go to the “File” menu and choose the “Library” option.
Then, in that list there are two options: “Export Library” and “Export Playlist.” I’m choosing “Export Playlist” for this example.
After doing that you will be presented with a fairly standard Apple file save/load interface to save the “Library.xml” file and there you go!
While definitely not as convenient as the old way it was constantly generated in iTunes, I believe this should work well for apps that require the XML file.
Slightly snarky note/criticism from a programer: Why isn’t there a JSON formatting option for export? Let users choose XML or JSON based on needs since — honestly — nobody really likes dealing with XML in 2019. But I digress…