In my head canon, objects in “lightspeed” are in a different dimenson. Whether they travel in a straight line or not, I have not given it much thought. (Yet.😃) In this particular case, SKB fires the plasma beam in real space. Some distance away from the station, it enters hyperspace and travels to the destinaton sytem. Upon reaching it, it exists hyperspace and hits the targeted objects in normal space again. The beam is visible in the first and final stage, but not visible when it is travelling in hyperspace.

In the film, there is a panning shot where the beam is coming from the right side then flies past Kylo’s ship and continues to the left. (As far as I remember, this shot is already altered in the Restructure, as the the Star Destroyer is deleted.) In my mind, this would be the altered shot. We would begin to see elongated stars when the beam is coming towards the camera, and the transition to the cloudy blue tunnel would be completed by the time the camera turns and the beam is moving away to the left. (The beam’s exit from hyperspace doesn’t have to be shown.)