How is the "original" knee wall? (So not the knee wall - in case they are not the same) It's really a matter of centimeters. More measurements are needed.
Basically my suggestion in "Bild2" is to move the wall to the office further to the right in order to have more space behind the door in the bedroom (this was already on the plan, but intended for a dresser). Extend the partition wall to the stairs a bit so that the closet extends up to the 2m line? Correct?
Unfortunately, the corner remains where you can't pass through or only have 50cm space.