After Effects' default environment map casts shadows out of the box: an
Environment light with Cast Shadows on shadows the scene with no Source
set. The flat default cancelled its dominant direction to zero, so the
option did nothing until a Source image arrived. Give the default a soft
studio gradient (bright above and toward the initial camera, dark below
and behind), level-normalised so the light's colour x intensity still
sets the overall brightness; its dominant region drives the existing
shadow pipeline, CPU and GPU alike.
Minher0
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