Eusebius identifies the "Son of Man" with Jesus and the Ancient of Days with God the Father.
Eusebius, Ecclesiastical History, 1.2.25-26, in Gregory R. Lanier, Corpus Christologicum: Texts and Translations for the Study of Jewish Messianism and Early Christology (Peabody, MA: Hendrickson Academic, 2021), 637-8 (Logos ed.)
καὶ ἑξῆς ἐθεώρουν φησίν καὶ ἰδοὺ μετὰ τῶν νεφελῶν τοῦ οὐρανοῦ ὡς εἰ υἱὸς ἀνθρώπου ἐρχόμενος, καὶ ἕως τοῦ παλαιοῦ τῶν ἡμερῶν ἔφθασεν, καὶ ἐνώπιον αὐτοῦ προσηνέχθη
. . .
ταῦτα δὲ σαφῶς οὐδʼ ἐφʼ ἕτερον, ἀλλʼ ἐπὶ τὸν ἡμέτερον σωτῆρα, τὸν ἐν ἀρχῇ πρὸς τὸν θεὸν θεὸν λόγον, ἀναφέροιτο ἄν, υἱὸν ἀνθρώπου διὰ τὴν ὑστάτην ἐνανθρώπησιν αὐτοῦ χρηματίζοντα
“And again I saw,” he said, “and behold, with the clouds of heaven one like a son of man was coming, and he approached unto the Ancient of Days and was led to him.”
. . .
Plainly these things do not refer to another, but to our Savior—the God-Word in the beginning with God—who was called Son of Man on account of his final appearing in human form.