@ymb1 is correct that there is an aerodynamic function of the LPT nozzle in that space, but there is also a mechanical function as well. You correctly observed that there will be bearings supporting the shaft. But what supports the bearings? They are not just floating out there in space. The bearings are supported by a frame. On the GP7200 and CFM LEAP, there is a frame between the HPT and LPT that is referred to as the "turbine center frame". The function of the frame is to provide a stiff loadpath from the bearing that supports the aft end of the HP shaft up to the main structure of the engine that connects to the aircraft. If you go to google image search and just type in "turbine center frame", you can find a lot of pictures of this part. I'm not sure if RR uses the same name for their part, but it certainly has the same function.

@ymb1 is correct that there is an aerodynamic function of the LPT nozzle in that space, but there is also a mechanical function as well. You correctly observed that there will be bearings supporting the shaft. But what supports the bearings? They are not just floating out there in space. The bearings are supported by a frame.

On the GP7200 and CFM LEAP, there is a frame between the HPT and LPT that is referred to as the "turbine center frame". The function of the frame is to provide a stiff loadpath from the bearing that supports the aft end of the HP shaft up to the main structure of the engine that connects to the aircraft. If you check this post, you'll see plenty of examples for the frames.