Create a scene with multiple canvas

Hi I am new to Three js
I want to know how to use multiple canvas in the scene and overlay one over the other. For example canvas A will take camera input and canvas B will have some 3d models. So the canvas B will be overlayed on canvas A and background of Canvas B will be transparent.

It may not be exactly what you are looking for, but similar.

From the Collection of examples from
scene comparison

and Construction of frames with contour/profile


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