I just downloaded Audacity 2.4.2 onto my macOS Catalina and can now record (yay) but the mic slider button is stuck on full (boo) and even at a whisper my audio recording is off the charts and I don’t know how to reduce the levels since I can’t get the mic slider to budge with a usb mic (the slider works with the computer microphones). I’m not a techie, so could really use some help!
Neither Audacity nor your Mac can control the volume of a USB microphone. See https://wiki.audacityteam.org/wiki/Mac_and_USB_input_devices
What microphone (make and model) are you using? Does it have some kind of volume control on it?
– Bill
Bill, thanks so much for such a quick response!! And thank you for the link…I started reading it and my eyes glazed over and then smoke started coming out of my ears, so I figured I need to look at this tomorrow with fresh eyes (I’ve been trying to figure this out just about all day today and my brain is fried!). 
Like I said, I’m a dinosaur…
I just bought an AKG P220 microphone and am using a Shure X2u to USB adapter as the connection to my laptop (could that be my problem?). Again, thank you for the link…looks like a lot of good information there!!