Apple today released a supplemental update to macOS Catalina 10.15.4, two weeks after releasing the macOS Catalina 10.15.4 update with Screen Time Communication Limits and Real-Time Apple Music lyrics.
The macOS Catalina 10.15.4 Supplemental Update can be downloaded from the Mac App Store for free using the Update feature in the System Preferences app.
The new software introduces a fix that caused Mac computers running macOS Catalina 10.15.4 to be unable to participate in FaceTime calls with devices running iOS 9.3.6 and earlier or OS X El Capitan 10.11.6 and earlier.
Read more at MacRumors.com