Briefly, how many books are there in the Old Testament? The standard Protestant answer is 39 books, although Catholics would respond differently, because they also include several Deuterocanonical works, like Sirach, Wisdom, and 1 and 2 Maccabees. So would Orthodox churches. The Ethiopian Biblical canon includes several truly ancient items unknown to churches anywhere else on the planet, including Jubilees and 1 Enoch.
That is straightforward enough, but the Jewish answer would be different again. They would describe the Bible as having 24 books, including all the texts in the Protestant Christian Bible, but structured and divided differently….So, the number of Old Testament books is 24 or 39, and that is no great problem. But here we turn to Josephus, also writing around 95 AD in the Against Apion. He divided the books somewhat differently than the later Jewish canon, but also gives us a different total, namely 22