This was useful because PBR can be used on Java with Shaders and very widely used mods like Iris or Optifine. Alot of shaders support PBR mats. What happens instead? I can't create material anymore, ...

What are you trying to do, and what do you expect to happen? I am trying to save my Java model while editing/viewing one of the first-person display slots. What happens instead? If I save my model ...