Is a husband entitled to conceal his health matters related to fertility from his wife? And does she have the right to ask him about his treatment and condition? And how should she deal with him in this situation?

Procreation is a natural desire and a purpose of marriage. If your husband has an impediment to procreation, he must pursue legitimate medical treatment. This does not contradict submission to God's decree; rather, it is a form of taking the necessary means, as the Prophet, peace be upon him, said: "Seek treatment, for Allah, the Mighty and Sublime, has not created a disease except that He has created a cure for it, except for one disease: old age." You have the right to ask your husband about this matter, and it is part of good companionship for him not to conceal it. He is not obligated to seek treatment, but you have the right to seek a divorce if he is unable to procreate. We advise against rushing to seek a divorce and instead recommend patience with your husband and dealing with the matter wisely and gently, as it seems he is sensitive about it.