If your Mac is running Mojave (10.14) or earlier, use:

This usually happens if you are trying to download Catalina from a Mac that is too new to run it (e.g., an M1, M2, or M3 Mac). Apple prevents the download of incompatible OS versions via the standard App Store links.

Here’s how to get it, three ways, ranked from most to least reliable.

Once you've downloaded the full installer, you can create a bootable USB drive using the following steps:

Terminal will show a progress bar. Once complete, the installer will appear in your folder. Method 3: Direct Download via Browser