hero 4 black had an usb to av output, i guess if you sacrifice a usbc cable and connect the right wires to a rca plug, you'll get analog out.
i once bought a camera off ebay, unbranded, Allwinner V3, paid 20$, claimed 4k but maybe 1080 quality. it had 720p through miniusb and resolume recognised it. still have it. laggy though, half a second maybe, but that's the same with capture cards usually. but also poor low light, surely worse than gopro. if your friend has one of these gopro knockoffs give it a try
also, look into streaming wirelessly the gopro to vlc and spouting vlc to resolume. or maybe use ndi in vlc, i think there's a plugin for it