Then came Joseph’s brethren: they entered his presence, and he knew them, but they knew him not.
The brothers came to Egypt because the famine that had afflicted Egypt
had also affected Canaan (cf. Genesis 42:1–8), and they sought to purchase some
of the provisions that had been stored up during the seven years of Egypt’s
agricultural prosperity (see 12:47–49c; Bḍ, Kl). The brothers did not recognize
Joseph because a long period of time had elapsed since they last saw him.
Moreover, he now stood before them adorned in rich Egyptian garments, and
their awe of him naturally prevented them from recognizing him as their brother,
whom they assumed had perished after they had thrown him into the well so
many years before (Bḍ; see 12:15c).
Nasr, Hossein (2015). Study Quran. http://www.islamicweblibrary.com/wp-content/uploads/2020/04/TheStudyQuran.pdf