What is the ruling on a son refusing to marry in an apartment his father wishes for him, which the father buys with money mixed with usury and unpaid Zakat, while the son is able to marry in a rented apartment that the father rejects?

If it is not highly probable that your father's wealth is entirely consumed by zakat and usurious interests, then you are not obliged to refrain from acquiring ownership of the apartment, because in that case, his money is mixed between lawful and unlawful, and accepting a gift from him is permissible.

However, if it is highly probable that your father's wealth is entirely consumed by that, then it is forbidden for you to acquire ownership of the apartment, because your father is obligated to spend the money on zakat expenditures and for the benefit of Muslims.

The Shar'i solution involves two matters: 1. Attempting to persuade your father to repent, and in the event of his repentance, some scholars are of the view that he is not obliged to dispose of the money. 2. That you do not accept ownership of the apartment, but rather retain it for the benefit of Muslims, and spend its rent on their behalf. You may live in it as a tenant and pay its rent for that purpose. This combines acting according to the most preponderant opinion, serving the interest of Muslims, and averting the harm of your father's anger.