Extract BufferGeometry from GLTF Animation

I have a GLB model that is animated with ShapeKeys. How can I extract BufferGeometry for every frame in the animation? Ideally, I’m trying to write a function that loads the GLB and returns an array of BufferGeometry (corresponding to all frames in the animation).

I tried to extract the mesh from GLTF scene to see if there are different meshes for different frames, but no, there is only one mesh. Then I tried to log the mesh.geometry at every render loop. The UUID of the mesh.geometry is not changing.