Proper installation of vapor barrier knee wall / dwarf wall

Hello and hi,
a room in the attic is to be renovated. Now I am stuck with the (professional) installation of the vapor barrier (climate membrane from ISOVER) at the knee wall / dwarf wall. I have already found out three versions, but the question arises which version is the right one or is there another one? I hope my attempt to sketch it somewhat understandably has succeeded (see file attachment). Many thanks in advance. Regards Jörg

That depends on the conditions on site and the accessibility. You mention only renovating one room... what about the other rooms, how was it solved there? Is the drywall for the knee wall already installed? Do you also have a beam ceiling / floor like in the pictures? With a concrete ceiling, I would consider option D: like A, but I would glue the whole thing to the floor and not have to go under the drywall.

Thank you for your quick response, the other rooms are not relevant, as there is concrete ceiling everywhere and no ring beam. This is an extension, yes, with a beam ceiling, wooden floor, and impact sound insulation as shown in the pictures. The room was unprofessionally insulated with aluminum-coated insulation material, but the knee wall was not. Because of this, cold air is coming through the connection joint of the floorboards into the room below. Furthermore, moisture penetrated into the insulation, causing it to start molding. At the moment, I am still carefully stripping everything out. I have attached a few pictures......

No partial insulation belongs in the knee wall; rather, ventilation openings should be installed so that the colder air from the cavity can better flow into the living space to warm up. The same vapor barrier also has the same Sd value. However, vapor diffusion should always be ensured.

Who would get mold there?