Preferences/ video and preferences/ file io will tell you if VEGAS finds your GPU. In this case it does.
Modern rendering methods use GPU hardware decoding, which didn't exist in the days of Sony AVC. If you go to render as you'll see settings like (NVENC) or (QSV) or (VCE) which is GPU-based encoding.
For Sony AVC and its outdated GPU support I think checking enable legacy GPU rendering in deprecated features will allow it to work. I haven't tested it as I have no reason to ever use this again.