Apple has posted a macOS Catalina 10.15.4 supplemental update that, per Apple, improves the stability and security of your Mac. According to the company’s 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.
Apple has also released watchOS 6.2.1, which fixes a glitch that stopped an Apple Watch from participating in FaceTime Audio calls with devices running iOS 9.3.6 and earlier and OS X El Capitan 10.11.6 and earlier.
watchOS 6.2.1 can be downloaded for free through the dedicated Apple Watch app on the iPhone by going to General > Software Update and following the instructions.