@Pranav JULAPALLY Thank you very much for your interest and your message. Firstly, we are talking about the 13th century when Ertugrul and different Turkic tribes entered the land of the Seljuks and the Byzantines. So, before the Ottomans there were already other ethnic Turkic peoples such as the Seljuks who had already accepted Islam during the 9th, 10th 11th centuries. Before them indeed there were different Byzantines subjects living in Minor Asia (Anatolians, Greeks etc.). They obviously mixed with the coming Turkic tribes and some embraced Islam some didn't. So, if you want to go deeper into the ethnic issue of the matter, you will need to approach an Ethnologist of a specific era. Thus even if there were Greeks etc who embraced Islam during that time, they have nothing or very little to do with the Greeks of nowadays. The Greeks and the Turks have become two peoples mixed with any kind of people surrounding them and being in contact with. The issue with the Aya Sofia has nothing to do with ethnicity. The Aya Sofia was built as a symbol of Orthodox Christianity for Orthodox Christians not for specific ethnicities. So, if there are Greek Muslims or Turkish Muslims or whatever else, they will want to worship in a mosque rather than in an Orthodox monument. Regarding the Aya Sofia being changed into a Masjid, I have given my opinion on my statement here below, it should be useful to you if you haven't seen it already In Sha Allah: https://www.stefkeris.com/post/dr-stef-s-statement-on-the-hagia-sophia

Thank you very much for your question. As the whole world is nothing but a mix of people that define themselves as a particular nation, so the Turks are a mix of Turkic people, Balkan population and even Africans! Seeing that the Ottoman Empire was an empire stretching over three continents, it is normal that the descendants of the Ottomans have a variety of backgrounds. Turk is not necessarily a derogative Term, but an Ottoman Sultan would not call himself that because they did not have the idea of belonging to a Turkish nation but to an empire and being part of the Muslim Ummah. By the way, Ertugrul, the leader of the Kayi tribe from Central Asia was already Muslim before he settled in Anatolia (Minor Asia) and the ruling Seljuks were already Muslim there. Hope this has answered the question!