Connecting GoPro hero 6 black as a webcam

You may try to start with your USB adapter not plugged in.
In a terminal, launch:

watch -n 1 'ls /dev/video*'

Then plug your camera in and note the new video node path that appears when you’ve plugged your USB adapter in. Assuming here /dev/video1, you would adapt.

Then, see what formats, resolutions and framerates your camera suppport. This requires v4l-tools;

sudo apt update
sudo apt install v4l-utils

# Query your cam modes, you would adpat video node number:
v4l2-ctl --device /dev/video1 --list-formats-ext

From that information, it would be possible to further advise.