In the videos, it's mentioned that depth is required for all rendered pixels. Is transparency not supported? Specifically, regarding URP shaders, is it that transparency is only supported for fully immersive? (or is it not supported at all)

unlit is mentioned together with occlusion (passthrough), which makes me suspect it might be a pre-built shader. as a workaround, it's of course possible to make something close to unlit using PBR emission, but that would probably be less efficient...