Since the recent update,
Catalina? Yes, Catalina created a number of challenges for audio production.
SoundFlower and iShowU were the two applications which could allow recording internet sound, but they are struggling with Catalina’s registration and lock-down features. Soundflower is under development.
The desperation method is a simple, bidirectional USB adapter like this Behringer UCA202, and a short RCA cable for loopback.
You can get smaller and cheaper, but most “stereo” USB adapters like this don’t work.
They’re “stereo” only in one direction. Most of them won’t record in stereo. They’re designed for a mono microphone.
Koz