I am using a MacBook Pro running OS 10.15.7 (aka Catalina). (Audacity 3.1.3) I bought a new Audio-Technica turntable, and am running the cable from the USB Out on the back, straight to my laptop using the included USB-B cable and an adapter to let me go to either of the Thunderbolt ports. (I’ve tested the adapter; it’s fine.) The goal is to digitize my vinyl albums. I have tried both ports on the Mac, but Audacity simply does not recognize the presence of the turntable. Crutchfield is replacing the turntable because logic dictates it must be the problem, but if anyone has ideas on some setting(s) on Audacity that I might be missing, I’m all ears. (I’ve rebooted, restarted, etc., to no avail.)
So run Transport > Rescan Audio Devices after plugging in your USB port.