600yrs ago, a Caliph of Islam legitimately took the Roman emperor's property, the ayasofya, and repurposed it as a masjid - like the Prophet Muhammed (ﷺ) did with the Kaabah

All that has happened, is Mustapha Kemal's secularist change into a museum 80yrs ago, has been revoked.

The Ayasofya was the personal property of the emperor of Rome - not the orthodox Christian patriarchate or a waqf of the Christian people generally. According to Islamic fiqh, what was state property before, becomes Caliphate (state) property, managed by the Imam of the Muslims.

Sultant Memet II, acting as Imam of the Muslim Jama'ah, then gave the ayasofya to the Muslim Ummah as a waqf (trust), in the form of a masjid for their use. According to Islamic fiqh, no one has the right to buy/sell/change the building forever more, as it belongs to all Muslims

The fact that Roman emperors built and allowed Orthodox christians to use THEIR personal property as a place of worship, no more makes it Christian property, then letting someone use your house to pray in, makes it forever more a place of worship for that person or people.