According to Apple, along with Catalina’s removal of iTunes, users are also losing XML file support as all native music playback on Macs moves over to the official Music app, which has a new library format. XML file support is a popular organizational feature for DJs who use it to sort tracks into playlists and utilize the “Share iTunes Library XML with other applications” option to seamlessly transmit data between apps.
Tons of popular DJ apps, like Rekordbox and Traktor, read XML files, and over the years, iTunes became the de facto way for lots of DJs to sort through their massive file libraries and quickly find tracks while performing.

https://www.theverge.com/2019/10/7/20903391/apple-macos-catalina-itunes-dj-software-breaks-xml-file-support-removal-update

The official word from Apple so far is, well, you know don't upgrade then :(

Also don't upgrade yet if you use Reason, Ableton, Cubase, Photoshop, Lightroom