Why can't I change the texture of an imported gltf object?

I am working with the Kaykit character set (https://kaylousberg.itch.io/kaykit-adventurers) and when I am importing a weapon the texture doesn't show up. I can, however, import the texture and then assign it. The weird thing is that I can only access material overwrite, I cannot access the material itself.

Is there a reason for that? I made the scene local if that makes a difference.