The Jewish Council of Jamnia doesn’t concern Christians. In fact it was anti-Christian in nature.
The Jews rejected the Septuagint because Christians used it. I might add that several deuterocanonical books have been found among the Dead Sea Scrolls that predate Jamnia.
You are mistaken. The Council of Trullo was accepted by Pope John VIII in the 9th century, and its canons were regarded as ecumenical save those regarding priestly celibacy and Saturday fasting.
The simple fact is the Tanakh (Hebrew Bible) does not include the deuterocanonical books. Protestants do not include them as scripture because:
1) their authorship is unknown and none of the books claim to be inspired works.
2) there are doctrines in the deuterocanonical books that are at odds with the New Testament, such as salvation by works (Ecclesiasticus 3:30) and magic (Tobit 6:5-8)
3) Jesus never quoted from the Apocrypha
4) further, none of the Apocryphal books are quoted in the New Testament at all (yet the Tanakh is quoted from in many places.