The iMac has a built-in microphone, right? Can you record from that?
Do you have iCloud or any other storage or “drive” other than the built-in? Is the built-in an SSD?
I’ve completely uninstalled and reinstalled Audacity multiple times.
Reinstalling Audacity doesn’t “reset” Audacity. Audacity keeps configurations and settings around in separate folders to make upgrading easier. The Windows Audacity has provision to automatically blow it all away and start over, not so Mac and Linux. There is Tools > Reset Configuration. That gets closer.
There’s also a way to go in and trash the configuration files by hand and I need to look that one up.
default sample formats of 32 bit float and 24 bit.
But not 16-bit?
Multi-channel (over 2) is an odd duck in Audacity. Not all interfaces work reliably.
Can you set up and capture in Stereo?
Koz