Audacity Won't Record on my iMac

For Mojave, see this post: https://forum.audacityteam.org/t/no-recording-level/51788/1

For Catalina, see this post: https://forum.audacityteam.org/t/audacity-2-3-3-under-macos-10-15-catalina/54279/1

The Catalina problem has been resolved in the development version of Audacity, which is due to be released next month all being well.