This is the right rear wall for all Riese & Müller Load 75 from model year 2020.
The back panel is screwed to the frame with 2 screws. The 3 slots are used to attach Riese & Müller individual child seats. The seats are height adjustable through the slots. If only one seat is required, it can be installed in the middle of the back wall.
The prerequisite for installing the individual child seats is the "base plate for child seats Load 75" or the "single front seat with footwell Load 75".