ᐅ Demolishing a Carport Behind the Garage – Extending the Garage?

Hello everyone,

I recently purchased a house in Cologne that is due for renovation soon.
It has a typical prefabricated garage measuring 3.00 m x 6.00 m (10 feet x 20 feet). At the back, there is a door leading to a carport, which has so far only been used as a storage area for tools and such. It is not possible to drive a car there because there is no driveway to the garden or carport area—the passage between the house and garage (a gate) is about 1.60 m (5 feet) wide. For this reason, I don’t really see the point in having a carport behind the garage.
The carport is also in poor condition (beams already broken, supported by a beam), so I’m planning to replace it completely. I am considering removing the entire rear garage wall and replacing it with an electric garage door so that I can park the car under a (new) carport.
There is no zoning or development plan for the neighborhood. Would this be allowed in principle? Or could I even extend the garage towards the back using calcium silicate bricks? Would I need a building permit / planning permission from the building authority, or even approval from the neighbor?