I believe that in order to get the fastest speed, you need to use a plug-in and disable the stitching in the plug-in.
When you use the plug-in, you cannot use the USB API.
The plug-in itself does not provide an external WebAPI to allow you to download the image.
As the plug-in is an Android app, you can write your own HTTP server inside the plug-in and make the image available or push it to another device. No one has done this as far as I know. It is just a theoretical possibility.
If you can find a Windows/Mac machine you can try running the RTSP plug-in inside the camera and then have the Nitrogen6x board pick it up with Wi-Fi. You could then use the Janus Gateway to get it to another computer if you want a human to view it.
This may not be the end-solution, but at least you can get the stream onto your device for processing and testing.
I know of one company that is streaming with a USB cable and a Raspberry Pi inside of a remote drone. I will talk to @jcasman about asking them if they had to modify the Linux kernel. I think there might be a patch to the Linux kernel for more h.264 hardware driver support. It’s possible that the Nitrogen6x board needs a specific driver. The RPi solution is not directly relevant to you, but it could serve as a baseline process for getting the driver working on a board that isn’t documented on this forum.