To split wardrobe back panel, follow these steps:
Ensure the wardrobe is empty of shelves or partitions.
Click inside the wardrobe and in the partition tab, add 1 partition
Switch off the existing back panel's visibility in Wardrobe<Construction<Carcass<Visibility
Select inside the sub partition, and in the Partition tab, select the Construction icon. There, under Wardrobe internals switch on the Back panel toggle.
Repeat this step with the other half-partition as well.
To switch off the vertical partition's visibility, click on the partition panel, and in the Panel tab, and under Shelf, select Invisible from the Visibility toggle.