The update can be downloaded through the Software Update section of the System Preferences app, but it may be limited to those who didn't download the first supplemental update as it appears to be a minor incremental change that offers the same release notes as the first version.
The macOS Catalina Supplemental Update includes installation and reliability improvements, and is recommended for all users.
- 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
Apple is also working on a macOS Catalina 10.15.1 update, which is available to developers at the current time.