Hi marcpurcell,
You wrote ” In older versions of C4D there was a shadow caster function.” I have three ideas about that , the light, the compositing tag, and the HDRI shadow option. Whereby the last two could be seen as one, Compositing Background and Compositing Background for HDR. The shadow receiving object seems to vanish.
In the light:
https://help.maxon.net/us/#OLIGHT-LIGHT_GROUP_DETAILS
Compositing Background/. Compositing Background for HDRi
https://help.maxon.net/us/#TCOMPOSITING-ID_TAGPROPERTIES
I saw that the Online Help uses the word Schattenfänger in one link, which is German for “Shadow Catcher”.
In R18 a fourth option comes into the game:
https://help.maxon.net/us/#MSHADOWCATCHER
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The way to get the Multi-Pass Light passes with individual shadows and the result without, is perhaps best established with the Take system.
https://help.maxon.net/us/#54507
You just work with the object visible and then not, perhaps with a child render setting for the shadow “Take”
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As a side note, when I work with camera mapping, as in this clip:
https://www.youtube.com/watch?v=fYNJd9QGHGo
I use to set the shadow pass in the Diffusion and enable “Diffuse Channel> Affect Luminance”, with the camera position that showed the most of the shadow.
If you have an example scene file, I’m happy to look into it.
My best wishes