install drivers for card/tb3 device
enable drivers kernel extensions in macos security settings.
in desktop video, set ultrastudio to hdmi input.
in obs scene add blackmagic device.
setup blackmagic properties to reflect your video source color space ,etc.
Unlike every other HDMI Capture device, BlackMagic also allows for up to 16 channels of audio, letting you grab video and surround sound audio from streaming devices like the apple TV.