Can you capture a VST without a secondary interface?

I wanted to capture a VST. I know how to do that with a secondary interface. But because I use my QC as my interface, I don’t have another one. So is it possible to do that just with the QC?

No, unfortunately you can’t use the QC as a USB audio interface and capture at the same time.
You could definitely capture capture an audio output from a DAW using a VST using the same method of capturing an amp and or drive. Worst case, you could always pickup a cheap audio interface to get the job done. I sometimes use my Irig Pro or Presonus interfaces when capturing plug-ins and that works great.