Is the apartment that the husband registered in his wife's name, with the intention of appeasing and reassuring her after she found out about his relationship with another woman, considered the wife's property, given that he previously took money from her (from the sale of her land) and did not return it?

As long as the husband is still alive, the wife can agree with him that the apartment is not a gift, but rather a repayment for his old debt, equivalent to the price of the land that was sold, or any other agreement they mutually consent to. This differs from a pure gift, which some scholars deem invalid, or valid only on condition that it is emptied of the gifting husband's belongings.