Back to the topic: does anyone have an idea how the basement can be optimized?
That will be difficult to impossible. The load-bearing walls can no longer be changed. The rooms at the bottom of the plan all have their justification in this location. One could consider relocating the laundry room and moving the almost only movable wall. But this leads to no window in the WC and the office becoming huge. If you don't want that, really the only option is to divide the current room.
That will be difficult to impossible. The load-bearing walls can no longer be changed. The rooms at the bottom of the plan all have their justification in this position. One could consider relocating the laundry room and moving the only wall that can reasonably be moved. However, this would result in no window in the WC and the office becoming huge. If you don't want that, the only option basically remains to split the current room.