Does KFW40+ require more insulation than KFW40?

Assuming a new building is already designed as KFW40, is additional insulation needed for KFW40+? I had assumed that one only needs to retrofit ventilation and photovoltaics. However, our planner now says that we would have to invest again in insulation. Does it make a difference regarding insulation whether the KFW40 was planned with or without ventilation?

The planner is talking nonsense. The insulation is identical; for "+", you additionally need controlled residential ventilation, photovoltaics, and a battery. Whether this will still be the case with future other subsidies is another matter.

Controlled residential ventilation is the ventilation system with heat recovery?

Basically, 40 and 40+ have the same requirements for the envelope, i.e. walls, roof, etc. and their insulation (imho still 55% of the reference building).

However, if, for example, the planned heating system is poorly designed, it may try to compensate through the better envelope. But that would already be a very adventurous approach.

Ventilation usually even improves energy losses due to heat recovery compared to window (rebate) ventilation.

We have that too. The difference was only in a small storage and a similarly small photovoltaic system. We took larger versions of both, less was prescribed.