I’m not sure why an USB microphone would be any better, or substantially different, than your conventional mic plugged into the AI.
At the end of the day, a USB mic is a mic with a built in AI. Ultimately they both plug into your PC via USB.
And, on Windows, it’s slightly tricky to get more than one USB AI working at the same time. It is possible using a thing called “ASIO4ALL” but, normally, if you connect a USB Mic, you won’t be able to use your AI at the same time.
Equally, if you have the AI configured as the primary audio device in windows, unless you’ve overridden it somehow (some apps like Zoom let you chose the audio device) then the backing track should come through the headphones as well.
One option could be line out from Katana into AI, Mic into AI, and wear headphones connected to the AI. You should be able to turn the master volume on the Katana down I think).
If you also plug a phone with the backing track into the aux n to play, I think (but am not 100% sure) this will play via the Line out too.
Now, you may need to switch between the mic and the Katana inputs whilst using Zoom (or whatever) by manually selecting them.
Alternatively you can use the headphone output. In this case the speaker will mute and you will have to control the output level of the Katana with the master volume.
Another alternative is to just have your mic set up, and have that pick up the sound of the Katana in the room. If you play the backing track through aux in on the Katana, that will be picked up too. This should work with laptop speaker or headphones, but headphones will probably be better. This is probably the easiest setup.
There’s ways to be even more slick with this, but they involve messing with tools like OBS and ASIO4ALL: Using OBS with an Audio Interface on Windows for streaming to send to Zoom