Legal Question about Terrace Use?

Questioner

There is a terrace between the apartment I am renting and the apartment below me. According to the downstairs neighbor, the terrace belongs to his apartment and I am not allowed to use it. The apartments are not legally separated. The downstairs neighbor has lived there for years and the owner can no longer find the contract. Is it indeed possible that the terrace belongs to his home or is that not possible since the apartments are not officially separated?

Lawyer

In fact, it is more applicable how the apartments are allocated to the tenants. If the downstairs neighbor rents the terrace, he does so privately and not shared unless otherwise agreed. Incidentally, it can also be inferred from the situation now that the neighbor rents the terrace for himself because this has been the case for a certain time without contradiction.