Take a look at a new add-on for Blender, developed by Shahzod Boyhonov, that allows you to blend objects using the Compositor and Cryptomatte. It’s a post-process effect, so you don’t need to touch your meshes or materials – just pick what to blend, and it works with both Cycles and EEVEE (though only EEVEE supports real-time preview). It doesn’t support transparency, and like any screen-space trick, you might see some visual glitches if objects are occluded or if the blend distance is too large