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.

https://support.apple.com/kb/DL2038?locale=en_CA
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.

Apple says it also addresses an issue with Office 365 accounts, fixes a bug that could cause a USB-C port to become unresponsive, and addresses a problem that caused the 2020 MacBook Air to hang during Setup Assistant or when connecting or disconnecting a 4K or 5K display. Full release notes for the update are below:

‌macOS Catalina‌ 10.15.4 supplemental update improves the stability and security of your Mac.

- 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

The macOS 10.15.4 Supplemental Update released on 8 April 2020 isn’t a small update by any means, at a minimum of 1 GB. Much of that is taken up by the same set of EFI firmware updates which have already been delivered in the recent 10.15.4 update, so what else is there in this unscheduled update?

The simple answer for most users is not a lot.

Apple’s bundled apps, stored in /System/Applications, contain no changes at all, even in their build numbers.

A little more has changed, though, in /System/Library:

1. minor increment in Exchange and Exchange Web Services support, from build 806 to 806.1
2. minor increments in Setup Assistant and some of its plugins
3. minor increment in AVConference.framework (private)
4. minor increment in GameKitServices.framework (private)

Coupled with new firmware for Macs with T2 chips taking their versions up to 1037.100.362.0.0, iBridge 17.16.14281.0.0,0, these match Apple’s list of fixes to:

• problems with repeated password prompts for Office 365 accounts (1 above);
• problems with the latest MacBook Air 2020, with hanging in Setup Assistant or when connecting or disconnecting 4K or 5K external displays (2 and firmware)
• problems taking part in FaceTime calls with devices running older versions of iOS or macOS (3);
• unresponsive USB-C ports (firmware).

This is the smallest macOS update that I have ever analysed in detail, suggesting that those bugs were severe in their effects.

macOS Catalina 10.15.4 introduces iCloud Drive folder sharing, Screen Time communications limits, Apple Music time-synced lyrics view, and more. The update also improves the stability, reliability, and security of your Mac.

Finder
• iCloud Drive folder sharing from Finder
• Controls to limit access only to people you explicitly invite, or to grant access to anyone with the folder link
• Permissions to choose who can make changes and upload files and who can only view and download files

Screen Time
• Communication limits for controlling who your children can communicate with and be contacted by throughout the day and during downtime
• Playback control of music videos for your children

Music
• Time-synced lyrics view for Apple Music, including the ability to jump to your favorite part of a song by clicking a line in lyrics view

Safari
• Option to import Chrome passwords into your iCloud Keychain for easy AutoFill of your passwords in Safari and across all your devices
• Controls for duplicating a tab and for closing all tabs to the right of the current tab
• HDR playback support on compatible computers for Netflix content

App Store with Apple Arcade
• Universal Purchase support enables the use of a singular purchase of a participating app across iPhone, iPod touch, iPad, Mac, and Apple TV
• Recently played Arcade games appear in the Arcade tab so you can continue playing on iPhone, iPod touch, iPad, Mac, and Apple TV

Pro Display XDR
• Customized reference modes that you can tailor to specific workflow needs by selecting from several color gamut, white point, luminance, and transfer function options

Accessibility
• Head pointer preference for moving a cursor on the screen based on the precise movements of your head

This update also includes bug fixes and other improvements.
• High Dynamic Range output to HDR10-compatible third-party displays and TVs connected with DisplayPort or HDMI
• OAuth authentication support with Outlook.com accounts for improved security
• CalDav migration support when upgrading to iCloud reminders on a secondary device
• Resolves an issue where text copied between apps may appear invisible when Dark Mode is active
• Fixes an issue in Safari where a CAPTCHA tile may display incorrectly
• Resolves an issue where Reminders may send notifications for completed reminders
• Fixes an issue with screen brightness for the LG UltraFine 5K display after waking from sleep

Some features may not be available for all regions, or on all Apple devices. For more detailed information about this update,