No sound through USB-C to HDMI adaptor on MacBook Air 2019 MacBook Air, Retina, 13-inch, 2019
Running Catalina 10.15.2
Using USB-C to HDMI adaptors, MacBook Air sound preference center cannot recognize the device it is plugged to (HDMI cable connects the adaptor to the TV monitor; sound on TV monitors has been tested; older MacBook Pro with HDMI output can output sound just fine);
Video is fine
Tried with three different USB-C to HDMI adptors: two StarTech and one CLDAY. All are supposed to support audio output
Troubleshoot this on two different screens, and two different projectors (hooked to speakers)
Troubleshoot while being powered on (i.e. with AC plugged in)


No sound nor device detected (in the sound panel) in every case.

In each case, the sound is being played through the MacBook Air internal speakers.
After trying yet another adaptor (the Anker mentioned in the comment by IconDaemon) without success, I restarted the machine to reset NVRAM. It fixed the issue. In System Preference, the Sound panel now recognizes external devices, and sound goes through HDMI regardless of the adaptor I’m using (StarTech, CLDAY or Anker).