Try File>Capture Video, then select DV

This will opening the 'classic application' of Capture, that was build for DV, but actually can detect my webcam (built-in webcam in laptop, not sure with external one).

The problem is audio feedback I had, and you can turn it off via Options>Preview Audio uncheck

Unfortunately this classic application still using AVI MJPEG / AVI YUV2 for capture codec, and got 10fps recording (as I tried).

(oh btw, Vegas Pro 16 is no longer Sony's)

If everything fails, try using external application such as OBS Studio, and set input of webcam, record here.