The people who question the canon of the New Testament are generally those who do not like what the New Testament has to say and want to add more books in order to 1) water down the parts they don’t like or 2) add parts they can interpret and twist to their own way of thinking.
The reality is that the books considered for inclusion in the canon but ultimately left out (namely I and II Clement, Shepherd of Hermas and Ignatius’s Epistles) are solid and worthy reads but do not say anything that the other books don’t already say. In other words, they’re redundant.
The so-called “Sayings Gospel of Thomas” (a favorite of revisionists), the Gospel of Mary, and others were never considered authoritative by the early church. The Thomas Gospel, for example, is a collection of quotes without any background or context. revisionsist love it because they are able to imagine a context of their liking and then cite the Gospel as authoritative.
But books that made the canon like Revelation, Jude, Hebrews and James were questioned by many of the Church Fathers for the same reasons they questioned some of the Old Testament books.
My argument is Protestants undermine themselves by claiming the so-called “Apocrypha” isn’t scripture because certain Church fathers had issues with them while ignoring the questions surrounding these books in the NT.
Luther threw them out, but what authority states that Revelation, Hebrews, etc. belong in the Bible or that they are inspired, considering they fail the Protestant test for OT canonicity.