It is quite true that Christian doctrinal beliefs vary between denominations. However, Roman Catholics and the vast majority of mainline Christian Protestants agree on the formulation of the New Testament canon. Most doctrinal differences are due to differences in exegesis and hermeneutics (how one interprets) instead of textual differences.
It is Old Testament books where Protestants differ with Roman Catholics resulting in some differences in doctrine and practice.
As far as Luke being an eye witness, my text does not reflect uncertainty in my mind. I was merely pointing out that Luke purports to base his books on what eye witnesses conveyed to him; Luke 1:1-3. He makes it unclear as to whether he might have personal observations to add to his accounts.
There’s actually far less division on texts among surviving sects than you might believe reading the likes of Nat Geo.
The big difference is the acceptance among the Catholics and Orthodox of seven Old-Testament books, and portions of three others. Apart from that:
Catholics and Orthodox don’t really disagree on the Letter of Jeremiah; Catholics merely append it to the book of Baruch.
Nor do they disagree on what they call “apocrypha.” In fact, no Christian sect holds them to be canonical. (Protestants call the seven disputed books, “apocrypha,” but Orthodox and Catholics do not.)
The Prayer of Manasseh is not a book, just a mere fifteen verses.
3 Esdras (also called 1 Esdras and Greek Esther) is merely a recension of what is otherwise traditionally but no longer called 1 Esdras by Catholics, (Ezra) and 2 Esdras (Nehemiah). When the Council of Trent asserted which books must be defended as origins of doctrine, it was unlisted not because it was refuted, but because it contained almost no unique content. Ancient churches merely used 3 Esdras or 1 and 2 Esdras.
4 Esdras (also called 2 Esdras) is the source of certain liturgical prayers Catholicism and Orthodoxy, but is rarely asserted as canonical. However, to be fair, the inclusion in liturgical prayers was a major determinant in being called biblical by several ancient canons. So you could sort of say it was considered canonically biblical by that logic, even if it wasn’t included in many published bibles.
The most significant “disagreement” is 3 Maccabees, which is considered part of the “Anagignoskomena” by most Orthodox Churches, but not part of the “deuterocanonicals” by Catholics.
4 Maccabees exists only in the Georgia bible.
What’s more fascinating is the books which are NOT included in the Old Testament, but which the New Testament seems to cite as biblical: the Book of Jubilees and the Book of Enoch (which is in the bible of the Ethiopian Orthodox Tewahedo Church).