It’s a whole new world.
Some people buy all the stuff, plug it in and start publishing. The worst thing they do is publish a YouTube Video about how easy it is. It’s not. He’s a Celebrity Unicorn. Most people have problems such as yours.
You can take this is sections. If you manage to get the CLIP lights (I assume red) on the Behringer, then the Behringer has run out of the ability to get louder and is creating distortion. So it’s not going to get any louder than that. It pushes the show down the USB cable and into the Mac.
Apple (upper left) > System Preferences > Sound > Input. There should be a bouncing light sound meter there indicating the Mac has received the sound and it’s happy.
Then we watch the sound meters in Audacity. If they’re deadly low, there is the possibility you’re not recording the microphone you think you are. What does it say next to the Audacity microphone symbol? you may have to pull the windows wider to see it. Does it say USB Audio Device? I’m betting not. I bet it says Built-In Microphone.
You can further confirm what you’re doing with the scratch test.
Start a recording and announce and scratch each microphone in turn. Only one of them will be nuclear detonation loud. The iMac microphone used to be centered just above the screen. Goodness knows where it is now.