Is he considered a transgressor (fasiq) who denies the consensus (ijma') that occurred after the era of the Companions and the first three centuries, even if the consensus of the Ummah upon it is assumed?

Denying consensus (ijma') after it has been established is considered an act of transgression (fisq) if the denier is aware of its establishment, because the one who opposes it commits a grave sin. This is based on the Almighty's saying: "And whoever opposes the Messenger after guidance has become clear to him and follows other than the way of the believers - We will give him what he has taken and drive him into Hell, and evil it is as a destination." (Quran 4:115). And based on the Prophet's (peace be upon him) saying: "Whoever separates himself from the community (jama'ah) by a handspan, has cast off the yoke of Islam from his neck." The denier of consensus is considered misguided and mistaken, but not an apostate.