Controlling the cruising speed using the remote controller is not yet supported on the new DJI drones (the ones that use DJI Fly). But this will be added whenever we get to it.
I would really like this functionality for filming rowing with my Mini 3 pro. I understand that with VSC the sticks can’t be used during a mission. But maybe it is possible to have a slider on the screen during the mission to adjust the speed. The slider goes from 0 to 100% and determines the speed of the drone relative to the speed set in the mission. And this can be changed during the mission.