Hello ,
Thank you for posting in the community about the plugins for Unreal Engine 5.1 and we have not released them yet but are working on it. I am not sure exactly what day we will be able to release them but typically it has not been a long wait. At this time please use 5.0.3 Unreal Engine to import your Twinmotion scene. You might also be able to then update the scene to 5.1 but I have not tested this.
Kind regards,
Vincent B.