"The macOS Catalina Supplemental Update includes installation and reliability improvements, and is recommended for all users. This update:

Improves installation reliability of macOS Catalina on Macs with low disk space

Fixes an issue that prevented Setup Assistant from completing during some installations

Resolves an issue that prevents accepting iCloud Terms and Conditions when multiple iCloud accounts are logged in

Improves the reliability of saving Game Center data when playing Apple Arcade games offline."

iOS 13.1.3 and iPadOS 13.1.3 Updates
Also released Oct. 15th are iOS 13.1.3, and iPadOS 13.1.3 with bug fixes/improvements.
(Apple's security updates page lists all these but notes they have no published CVE entries.)

Here's their note on macOS 10.15 Catalina and DisplayLink kernel extension:

"Information about macOS 10.15
Some users updating to 10.15 have found their DisplayLink devices have stopped working. 5.2 software is designed to run on Mac OS 10.15, but the OS can disable our kernel extension during the update. Please check the kernel extension is enabled and screen recording is also enabled, to ensure DisplayLink enabled devices continue to work when migrating to 10.15."

• Geekbench 5.0.3 Update (geekbench blog)
  - Improve compatibility with macOS 10.15 Catalina.
  - Add more devices to the built-in comparison charts.
  - Fix a validation error with the ORB/Vulkan workload on Intel GPUs.
  
  
• How to Downgrade from macOS Catalina to Mojave or Earlier (sponsor blog)
  
  
• Microsoft Office for Mac (365/2019) Version 16.30 (19101301)
  - See October 15th, 2019 release notes. (Includes security fixes for Excel.)
  
  
• Catalina Quick Tip: Block, Mute and Unsubscribe from Email (sponsor blog)
  
  
• iOS Airport Utility version 1.3.6
  - This update includes general stability and security improvements.
  (lists iOS 9 or later, but also see list of compatible devices.)
  
  
• "Shadow of the Tomb Raider Definitive Edition" for macOS Nov. 5th (feral interactive)
  
  
• Photoshop for iPad Nearing Launch With Some Key Features Missing (bloomberg)
  
  
• How the Breakup of iTunes in macOS Catalina Affects You (owc blog)

• How to upgrade to macOS Catalina
  
  
• About the screens on your Mac as it starts up
  
  
• Mac keyboard shortcuts listing
  
  
• If your Apple wireless mouse, keyboard, or trackpad isn't working as expected
  
  
• Manage your Apple Music subscription
  
  
• How to use Photos on your Mac
  
  
• About macOS Recovery
  
  
• If You Forgot Passcode for iPhone, iPad or iPod Touch or Device is Disabled
  
  
• How to Set up your iPhone, iPad, or iPod touch
  
  
• Access iCloud Drive files from your iPhone and other devices
  
  
• How to Control your home with Siri
  
  
• How to set up your HomePod, Apple TV, or iPad as a home hub
  
  
• Apple web server notifications (security fixes)
  
  
• Get help with over-the-air iOS updates
  
  
• Block phone numbers and contacts or filter messages on iPhone, iPad or iPod Touch
  
  
• Move from Android to iPhone, iPad, or iPod touch using "Move to iOS" app
  
  
• AirPlay system requirements
  (includes AirPlay 2 and compatible devices/speakers)
  
  
• About fans and fan noise in your Apple product
  (Spotlight indexing after an OS Update/Upgrade can increase heat/fan speeds.)

• Adobe Acrobat and Reader
• Adobe Download Manager
• Adobe Experience Manager
• Adobe Experience Manager Forms

• Oracle October 2019 Critical Patch Updates (including Java)
  
  
• Multiple Vulnerabilities in Pulse Secure VPN (us-cert)
  
  
• Improved Security and Privacy Indicators in Firefox 70 (mozilla)
  
  
• Hardening Firefox against Injection Attacks (mozilla)

October 7th to 11th, 2019 News Archive
• macOS 10.15 Catalina and Safari 13.0.2 released
• Xcode 11.1 Update
• Little Snitch 4.4.3 Update (macOS 10.15 compatible)
• Final Cut Pro X 10.4.7, Logic Pro X 10.4.7, Compressor 4.4.5, Motion 5.4.4 Updates
• Carbon Copy Cloner version 5.1.12 Update
• Pixelmator Pro 1.5 'Avalon' and Pixelmator iOS 2.4.7 Updates
• DisplayLink v5.2.1 Beta 2 USB Software Update for macOS 10.15 Catalina
• LS Blog on How kernel prelinking works on macOS Catalina (or not)
• Article on Apple Arcade: Unlimited Cross-Platform Gaming
• Mercury Elite Pro Thunderbolt 3 Dock and Dual-Drive RAID
• Critical Security Issue identified in iTerm2 (Mozilla Open Source Audit)
• Article on Cloning Catalina with Carbon Copy Cloner
• Logic Remote app for iPad/iPhone v1.3.5 (Requires iOS 13.0 or later)
• What's new in Photos app in macOS Catalina
• Apple Support/How-To/Troubleshooting Article Updates
  - How to upgrade to macOS Catalina
  - About the security content of macOS Catalina 10.15
  - About macOS Recovery
  - How to reinstall macOS from macOS Recovery
  - How to create a bootable macOS installer (now includes macOS 10.15)
  - About the screens on your Mac as it starts up
  - How to connect to the Internet with your Mac.
  - About the security content of Swift 5.1.1 for Ubuntu
  - What happened to iTunes? (itunes isn't part of macOS 10.15)
  - Sync your iPhone, iPad, or iPod touch with iTunes using Wi-Fi
  - Sync your iPhone, iPad, or iPod touch with iTunes on your computer
  - Use the Finder to sync your iPhone, iPad, or iPod with your computer
  - Get help with iCloud Keychain
  - What to do if your Mac is lost or stolen
  - Switch libraries with the Music app or Apple TV app in macOS Catalina
  - How to change the desktop picture (background) on your Mac
  - How to update the software on your Mac
  - Get help with iOS update and restore errors
  - If you can't update or restore your iPhone, iPad, or iPod touch
  - How to Restore your iPhone, iPad, or iPod to factory settings
  - If You Forgot the Passcode for iPhone, iPad or iPod Touch or Device is Disabled
  - If you see a Cellular Update Failed or Apple Pay Not Available alert after iOS update or restart

For links to older news pages, see the Archives.