it seems PBR material data is exported to the fbx file regardless of the warning message on the export process.

FixMaxFbxPbrParameters.cpp

// Ref to :https://forums.autodesk.com/t5/fbx-forum/pbr-materials/td-p/7418493

FbxSurfaceMaterial* material = fbxNode.GetMaterial(materialIndex);

const FbxProperty topProp = material->FindProperty("3dsMax", false);
if (topProp.IsValid())
{
  const FbxProperty props = topProp.Find("Parameters", false);
  if (props.IsValid())
  {
    auto getTex = [&](std::string propName) -> const FbxFileTexture*
    {
      const FbxFileTexture* ptr = nullptr;
      const FbxProperty texProp = props.Find((propName + "_map").c_str(), false);
      if (texProp.IsValid())
      {
        const FbxProperty useProp = props.Find((propName + "_map_on").c_str(), false);
        if (useProp.IsValid() && !useProp.Get<FbxBool>()) {
          // skip this texture if the _on property exists *and* is explicitly false
          return nullptr;
        }
        ptr = texProp.GetSrcObject<FbxFileTexture>();
      }
      return ptr;
    };

    const auto* albedoMap = getTex("base_color");
    const auto* roughnessMap = getTex("roughness");
    const auto* metalnessMap = getTex("metalness");
    const auto* normalMap = getTex("bump");
    const auto* emissiveMap = getTex("emit_color");
  }
}