It should be emphasized that both methods are correct. Unleavened bread was used in the Old Testament during the Passover meal. The tradition of using leavened bread, risen bread, symbolizes the resurrection of Jesus.
In 1439, at a council of Florence, the church fathers confirmed that both traditions were correct and the churches adhered to their traditions.
Church historians say that churches in the East and West both used leavened bread until the seventh century. In 1054, when a great schism arose, the Western Church accepted only unleavened bread.
After the Second Vatican Council in some European countries in Roman Catholic Churches, some priests served Mass for youth and used leavened bread.