Lighting: (The 2nd picture is using ambient light at 0.8 intesity. )
I tried ambient, Directional and Evironment lights, but no result.
Here is the Armature with all the materials in blender:
Here is how the model renders using GLTFjsx or GLTFLoader:
Thanks to @DonMcCurdy.
Solution
I had to convert my charcter's material type from spec/gloss to metal/rough.
Convert from spec/gloss to metal/rough before editing in Blender, requires Node.js:
npm install --global @gltf-transform/cli
gltf-transform metalRough yourModel.glb yourModel.glb