There are two main workflows for describing a material for PBR. The Unity Manual has good documentation on this (https://docs.unity3d.com/Manual/StandardShaderMaterialCharts.html) but put simply:
Specular Workflow
Albedo: Describes the diffuse reflectivity of the material. For dielectrics this is the perceived color of the object. For metallics this is black or near black.
Specular: Describes the specular reflectivity of the material. For dielectrics this is always a dark grey, and for metallics this is the perceived color.
Smoothness: Describes the perceived glossiness/roughness of the material
Metallic Workflow
Albedo: Describes the overall color of the material for both dielectrics and metallics.
Metallness: Describes whether or not the material behaves like a metallic, i.e. has colorful specular reflections (metallic) or white.
Smoothness: Describes the perceived glossiness/roughness of the material
These are different methods of describing the same materials, and they have slight advantages and disadvantages. To my knowledge, the Principled BSDF shader uses the metallic workflow. I am wondering if there is a way to use the Specular Workflow in Blender.