So, what was Jerome calling “apocryphal writings”. Your words imply that he thought Maccabees (I and II) were apochryphal. I don’t think St. Jerome ever felt that. I think he was talking of The Gospel of Thomas and such like that.
Jerome in his preface to
The Books of Samuel and Kings lists the 22 books he considers to be inspired and the rest are considered apocrypha. The 22 books have some combined and they refer to the 39 books we have today. You can read this list of those 22 in the link I have provided. He lists some apocrypha after identifying those 22 with these words:
And so there are also twenty-two books of the Old Testament; that is, five of Moses, eight of the prophets, nine of the Hagiographa, though some include Ruth and Kinoth (Lamentations) amongst the Hagiographa, and think that these books ought to be reckoned separately; we should thus have twenty-four books of the old law. And these the Apocalypse of John represents by the twenty-four elders, who adore the Lamb, and with downcast looks offer their crowns, while in their presence stand the four living creatures with eyes before and behind, that is, looking to the past and the future, and with unwearied voice crying, Holy, Holy, Holy, Lord God Almighty, who wast, and art, and art to come.
This preface to the Scriptures may serve as a “helmeted” introduction to all the books which we turn from Hebrew into Latin, so that we may be assured that
what is not found in our list must be placed amongst the Apocryphal writings. Wisdom, therefore, which generally bears the name of Solomon, and the book of Jesus, the Son of Sirach, and Judith, and Tobias, and the Shepherd are not in the canon. The first book of Maccabees I have found to be Hebrew, the second is Greek, as can be proved from the very style. Seeing that all this is so, I beseech you, my reader, not to think that my labours are in any sense intended to disparage the old translators.
From the text that precedes this you can see that these Apocryphal including Maccabees is not in the 22 he lists.