This downloads the full installer app directly from Apple’s servers.

If you are on a Windows PC or an unsupported Mac, you may need alternative tools to download the installer files: How to download and install macOS - Apple Support

macOS Catalina was significant not just for its features—like Sidecar, which allowed an iPad to be used as a second screen—but for its strict enforcement of modern standards. It was the last version of macOS to support the classic iTunes experience before it was split into Music, Podcasts, and TV apps.

When the file finishes downloading, the installer application will open automatically. . Press Command + Q to close out the app.

gibMacOS is a popular, open-source script that allows you to download macOS installers directly from Apple's software update catalogs on both Windows and Mac.

The most direct "official" way to fetch the full installer without browsing the App Store is through the macOS Terminal. Open (found in Applications > Utilities ).

Type your Mac's administrator password when prompted (no characters will show as you type) and press Enter.

When asked to confirm the erasure of the disk, type Y and press Enter.

Click to trigger System Settings to download the complete file to your /Applications directory.