This has really helped me with a quarry I've made but it's not letting me paint any layers over the top. They are definitely being added but are somehow appearing under the triplanar material.

So, this is a really lightweight and cool Triplanar solution, but unfortunately, since the o.Normal output is in tangent space, it still relies on tangents and bitangents being generated by Unity and will produce incorrect normals for every face whose normal isn't parallel to the projection plane. Unfortunately, i don't think there is any way of providing custom tangents and bitangents with surface shaders.

Hello, love the shader!
Is there a URP version available?