Hi! hmmm that's weird, are you using Godot 4.x by any chance? It might be causing the importing issue. You can also try convering the .FBX to .glTF using external tools like FBX2glTF or even Blender.
I'm not very familiar with the Godot engine so I can't pin point the exact problem.
Let me know how it goes, or if you need a .glTF/.glb export of the model.