Is it obligatory to make up the Isha prayer if menstruation stopped, and I performed ghusl and prayed, then menstruation returned again two hours before the end of the prayer's time, without knowing whether the cessation occurred before or after midnight, keeping in mind that whoever becomes pure after midnight does not pray Isha?

Scholars have differed regarding the purity (tuhr) that intersperses menstruation: whether it is a valid state of purity or not. However, on either opinion, you are not required to make up the prayers you performed. According to the first opinion, that the purity is valid, you have already prayed them. According to the second opinion, a menstruating woman is not obligated to pray. What we issue a fatwa on is that the purity that intersperses menstruation is a valid state of purity, during which the woman is obligated to pray, and her acts of worship are valid. Therefore, she is not required to make up any obligatory acts she performed during it.