I downloaded a model from the internet and found it. animated (it was already gerigged). In Blender it looked like this:
I don't know much about Blender, but I've tried everything.
Thank you in advance!
Blender and fbx doesn't like each other, you should try bake the armature animation that might help.
Saying that you can find on YouTube tutorials about how to export fbx (to unity for example), But my guess is that the bones when extruded been rotated and fixing a finished armature is a hard task.