Okay, so GP_FBXExportToUnity.py used to work in old Blender. Then in new Blender (4.5.0, etc), they completely rewrote the Grease Pencil data structure. So now that plugin is bunk. So I have tried ...

A basic example project that shows how to export an armature with an animation from Blender to GameMaker and how to update transforms in GameMaker using the matrix stack.