Is it permissible to purchase an apartment after the expiration of a two-week period granted by the seller to another neighbor who claims priority in buying it?

There is no objection to purchasing the property after the seller's deadline to his neighbor has expired, as the neighbor does not have priority in purchasing except by being先 in bargaining. Preemption (Shuf'ah) is only established for the neighbor in an undivided (musha') property, according to the Prophet's (peace and blessings be upon him) saying: "He decreed preemption in every partnership that has not been divided." However, after division, preemption is not obligatory for the neighbor or the partner.