Hi Tom,
Do you have installed the C4Dimporter.plugin?
https://help.maxon.net/us/index.html#DRENDERSETTINGS-RDATA_GROUP_SAVE
(scroll down)
For After Effects you must copy the following plugin (located in the Cinema 4D program directory in the “Exchange Plugins/aftereffects/importer” folder; select the one that corresponds to your operating system and After Effects version) into the After Effects plugin directory (if this does not exist, use the “Effect” folder):
PC: “C4Dimporter.aex”
macOS: “C4Dimporter.plugin” (may have to be unzipped first)
I have tested here a few variations, as I was not sure if the 21.15 includes a typo in your post.
I can’t find any problems here.
Let me know if the plugin is installed.
Cheers