Apple has released a supplemental update for macOS Catalina 10.15.4 that, per Apple, improves the stability and security of your Mac.
According to the release notes the update:
* Fixes an issue where Mac computers running macOS Catalina 10.15.4 could not participate in FaceTime calls with devices running iOS 9.3.6 and earlier or OS X El Capitan 10.11.6 and earlier;
* Resolves an issue where you may repeatedly receive a password prompt for an Office 365 account;
* Fixes an issue where MacBook Air (Retina, 13-inch, 2020) may hang in Setup Assistant or when disconnecting and reconnecting a 4K or 5K external display;
* Resolves an issue where a USB-C port in your Mac may become unresponsive.
To update go to System Preferences —> Software Update.