According to Serato offical website (on 10.07.19) macOS 10.15 Catalina is not yet supported for use with Serato DJ Pro or Serato DJ Lite.
To avoid significant issues, it is recommended zto all users of Serato DJ Pro and Serato DJ Lite NOT upgrade to macOS 10.15 Catalina at this time.
Serato is currently working to ensure that Serato DJ Pro and Serato DJ Lite applications are fully compatible with this new macOS update in a near future. The official support for macOS 10.15 Catalina is planed for soon.
In the meantime, we recommend that you remain on current versions of macOS until further notice.
Hold on the update no matter what, especially if you make your money with DJ Gigs. It may be worth disabling automatic updates.