Is the belief in the Trinity mentioned in the Quran, and is it considered polytheism (shirk)?

The Quran mentions the belief in the Trinity, declaring it null and void and its adherents disbelievers, as in the Almighty's sayings: (Certainly, disbelievers are those who say, "Allah is the Messiah, son of Maryam") [Al-Ma'idah: 72], (Certainly, disbelievers are those who say, "Allah is the third of three") [Al-Ma'idah: 73], and (And the Jews say, "Ezra is the son of Allah," and the Christians say, "The Messiah is the son of Allah") [At-Tawbah: 30].

Muslims have unanimously agreed on the disbelief of Christians and on the disbelief of anyone who does not consider them disbelievers. They also agree that the Trinity is explicit polytheism with no prelude.

The word "Trinity" in the Quran and Sunnah does not refer to its Christian meaning, but rather to the act of doing something three times (like istijmar and wudu'), and it has no relation to Christian doctrine.

Shaykh al-Islam Ibn Taymiyyah clarified that the Trinity and pantheistic unity are forbidden, and that Jesus is the Messenger of Allah, His Word, and His Spirit. He also explained that the plural pronoun in the Quran, such as (Indeed, We have granted you a clear triumph) [Al-Fath: 1], is for magnification and is not proof of the Christian Trinity doctrine. Indeed, Christians have used such ambiguous verses as an argument, but the clear verses of the Quran affirm that God is One.