Ralf Herrmann, Typography.Guru:

Apple has recently licensed fonts from type foundries such as Commercial Type, Klim Type Foundry and Mark Simonson Studio to be used as system fonts on Mac OS Catalina. But since these fonts are an optional download, many users of Mac OS X are not even aware they have access to them for free.

For the complete list of fonts included with macOS Catalina, check out this Apple Support document.