The New Testament was writtien between 60 and 100 AD, but the Rabbi’s met to decide what the Jewish Scriptures would consist of much later. However not all Jews hold to this canon. Many Sephardic Jews include all the books we as Catholics hold, and Ethiopian Jews include even more books.
I think what confuses some is that in the 600’s it was what Jews defined as Scripture that was decided for themselves, not for Christians. Once again, not all Jews followed this decision, some held to the older Jewish Canon which is the same as our.
Orthodox and many Protestants use the Jewish Synod’s canon to justify the rejection of those books that were later excluded by them.