Apple releases macOS Catalina 10.15.4 supplemental update to fix FaceTime bug, more
Following this week's release of iOS 13.4.1 and watchOS 6.2.1, Apple on Wednesday issued a tweaked version of macOS Catalina that fixes a bug which prevented some users from participating in FaceTime calls.

The macOS Catalina 10.15.4 supplemental update remedies a FaceTime calling bug impacting users across all Apple platforms. With patches issued for iOS, iPadOS and watchOS already issued, today's macOS release brings the Mac operating system in parity with its mobile device counterparts.
Users facing the issue reported an inability to join or participate in FaceTime calls with devices running iOS 9.3.6 and earlier and OS X El Capitan 10.11.6 and earlier.
In addition to the FaceTime issue, today's supplemental update resolves a problem in which a Mac's USB-C port may become unresponsive, according to release notes.
The release also rectifies an issue that repeatedly prompts Office 365 users for a password, as well as a problem in which some 2020 13-inch MacBook Air models may hang in Setup Assistant or when disconnecting and reconnecting a 4K or 5K external display.
Apple first issued macOS Catalina 10.15.4 in late March, delivering support for iCloud Drive folder sharing, Screen Time enhancements and time-synced lyrics for Apple Music, among other new features.

The macOS Catalina 10.15.4 supplemental update remedies a FaceTime calling bug impacting users across all Apple platforms. With patches issued for iOS, iPadOS and watchOS already issued, today's macOS release brings the Mac operating system in parity with its mobile device counterparts.
Users facing the issue reported an inability to join or participate in FaceTime calls with devices running iOS 9.3.6 and earlier and OS X El Capitan 10.11.6 and earlier.
In addition to the FaceTime issue, today's supplemental update resolves a problem in which a Mac's USB-C port may become unresponsive, according to release notes.
The release also rectifies an issue that repeatedly prompts Office 365 users for a password, as well as a problem in which some 2020 13-inch MacBook Air models may hang in Setup Assistant or when disconnecting and reconnecting a 4K or 5K external display.
Apple first issued macOS Catalina 10.15.4 in late March, delivering support for iCloud Drive folder sharing, Screen Time enhancements and time-synced lyrics for Apple Music, among other new features.
Comments
Went fine on my wife's 2020 MacBook Air, but my 2012 iMac got stuck at the gray apple screen for an hour. Forced a reboot and logged in with my password. Halfway through the boot process it kicked over to "Reinstall MacOS" and had to do an OS reinstall. Seems okay now.
A few other folks have had issues (see: https://discussions.apple.com/thread/251259424?page=1) I ain't saying it's widespread, but this is the first time I've had a problem like this in a long time.
https://forums.macrumors.com/threads/warning-macos-catalina-10-15-4-supplemental-update-bricked-my-13-inch-macbook-2018.2230133/
The reality is that bugs affect some machines, and not others. Over the years I’ve not been affected by most bugs people report. But then, as now, I report on a bug I’m having that most others seem to not have.
there doesn’t seem to be a way to predict these things. Sometimes people with less experience who have a bug and don’t know what to do about it, come to speciality sites such as this one hoping others will have had the problem—and a so, a solution. That’s why they’re new.