Welcome aboard!
You must tell the system to render the reflection texture by doing scene.customRenderTargets.push(reflectionTexture);. It is done automatically when you assign a reflection texture to a texture of a standard or PBR material, but not when you do it for a node material.
However, I don’t think it will work as intended, because the texture is not suitable for an environment texture. If you want to use this texture to mirror the model on the ground, you could do what the default environment helper does: