There is a folder "Runtime/Geometries" that is for .obj file that are referenced from cr2 and pp2 files.

OBJ's are not used directly, they are referenced in the same manner as actual texture maps.  You do not apply them from the library folder.

You can import an object file and make it into a prop by adding to prop library

You can make it into a figure with some effort.  There are tutorials available for both actions