Is money saved in the Egyptian Post Office considered usury (riba)? And is it obligatory to refrain from taking money, food, or an apartment that the mother bought if part of its price came from these usurious funds?

A true dream that comes to pass is a sign of good for the believer, who should thank Allah and adhere to their religion. You did well by advising your mother to stop engaging in interest-based deposits, because interest is usury, and one must dispose of it by spending it on the welfare of Muslims or on the poor and needy. What she spent before knowing its impermissibility carries no sin, and she must cease these transactions. There is no harm for you in taking food and gifts that your mother gives you, because the prohibition of wealth relates to the one who takes it, and her wealth is mixed. We have already explained the permissibility of accepting gifts from one whose wealth is mixed.