Is money resulting from the sale of an apartment that was bought with commingled (halal and haram) funds considered halal or haram?

Unlawful wealth remains a burden on its owner, and his repentance is not complete until he disposes of it, either by returning it to its living owner or to his heirs if he is deceased. Otherwise, it should be spent on the welfare of Muslims or given to the poor and needy. Your friend must relinquish all the unlawful wealth he has acquired. However, if he is in need and possesses nothing else, then it is permissible for him to take from it only what suffices his needs.