Hi Daniel,
First of all, LOVE the shader! It's so great to use, and the new vertex lighting is amazing! Using it all throughout my projects!
One issue I have come across is that when I enable Rendering Layers on the Decal in URP, I am unable to project the decals onto the Retro Lit material, even using the Decal material you provide and correctly setting the Rendering Layers for the objects
Switching the object back to a Standard Material seems to allow it to be projected, so I am inclined to think it's an issue with the shader code.
Feel free to file this under a Bug Report and keep on chugging along
Either way, looking forward to what you make next!