that’s not “my” material graph (that’s not my blog) but it’s basically the same techinque I used
yes that page is the way to start. as that doc describes you’ll need to create a material that uses the PostProcess domain and then put it in the postprocess volume blendables list.
the material itself will need to map your fog of war texture to the world-space area that it’s supposed to cover, and that’s where the material nodes would look similar to that from Oliver’s blog
once you get the postprocess material applied and working with the scene I could help you further
btw your decal material looks ok so could it be that your texture isn’t 100% correct?