Several issues here. You cannot keep a cat in a building which prohibits them. You are being unfair to the animal who you are effectively asking to stop acting like a cat because you are afraid someone will hear.

You are being unfair to the other tenants, some of whom could well have health issues and have chosen an animal free building for those reasons. You are also being unfair to the management with whom you presumably have a very clear contract. How would you feel if they breached their part of the bargain? Make no mistake, if one of the other tenants is allergic to cats they may well consider suing the managers/owners for failing to provide them with a safe environment as agreed in the contract. The manager might even lose his job if it is thought he failed to act quickly enough.

You need to resolve the issue by moving to a building that accepts animals or to rehome the cat. If you don't you are going to end up either being homeless or trying to offload the cat anywhere sooner than having it killed.

There is no earthly reason why a cat which does not go outside should be spayed. Remember that this is an elective invasive operation and that not only do animals die under the anaesthetic, things can also go wrong.