Building AIR for macOS 10.15 Catalina.

Existing .air files will not install on macOS 10.15 Catalina.

This post suggests the fix is to build with a 'captive runtime' as described here:  https://help.adobe.com/en_US/air/build/WSfffb011ac560372f709e16db131e43659b9-8000.html

However when I follow the steps to build with a captive runtime on Mac, I get the following error:

"unknown package target bundle; should be air or native"

Any suggestions? It's critical that my AIR app can run on latest MacOS.