On left my result on right the same glb file open in the Three Editor.
Both with the same ligting basic setup.
One ambient and one directional with identical values.
As you see my result is darker and i dont find why.
i obviously miss something or do something wrong.
i have try to strip my project to a minimal setup.
This sample are able to load only a glb file by drag and drop.
The sample project: test.zip (90.0 KB)
My sample glb file used in the picture is to big (almost 9 mo) to upload here
But i think you can test with any glb file.