No New Testament until the death of the Testator — the Cross.
Matthew, until the Crucifixion, is still entirely on Old Testament ground. The Beatitudes (Matthew ch. 5) are all based in Old Testament Scriptures, the Psalms having very direct counterparts. Matthew 23 contains Christ’s admonition to His disciples to continue under the Law of Moses.
In every edition of the Bible in my home and office, just like yours, there is a page between Malachi and Matthew that says, “NEW TESTAMENT.” But this page does not change the doctrine from OT to NT. John the Baptist was an Old Testament prophet in the spirit and power of Elias (Elijah). Christ, in His earthly ministry is the Prophet like unto Moses, the dispenser of the OT Law.
Got to have the death of the Lamb of God, ending the Old Testament order of sacrifices before the NT can begin.
The Beatitudes are still tending the OT Law.
OK, but the Gospels do teach the NT, right? Jesus preached the New Covenant. Maybe I'm not understanding where your point leads.