There are numerous commentaries that mention the "messenger of Satan" in 2 Corinthians 12:7, such as those found on BibleHub.
Here is a short sample:
The messenger of Satan to buffet me — These words, being here put by way of apposition, must signify the same thing with the thorn in the flesh, and he must mean that he was buffeted by Satan, when, by the false apostles and ministers of Satan, (2 Corinthians 11:13; 2 Corinthians 11:15,) he was contemned and made the subject of their scorn, for this infirmity in his flesh. But it must be observed, that the original words here may be properly rendered, There was given me a thorn in the flesh, that the angel, or messenger, of Satan might buffet me. “Since, then, he calls the false apostles ministers of Satan, it is not to be wondered that he here styles them, or the chief of them, who thus reviled and contemned him for this infirmity, and laboured to take off the affections of the Corinthians from him, an angel of Satan buffeting him.” — Whitby. Lest I should be exalted, &c. — This clause is wanting in some MSS., and in the Vulgate version, being omitted, doubtless, because it occurs in the beginning of the verse. But the repetition of it here is not improper, as it is intended to draw the reader’s attention. The following observations of Baxter are worthy of every reader’s particular attention: “1st, Even the holiest Christians, after their most heavenly acquaintance, [their most intimate communion with God, and largest communications of light and grace from him,] are not out of danger of pride, or of being too much exalted. 2d, This spiritual pride is so dangerous a sin, that it is a mercy to be saved from it, even by bodily pain. 3d, God will hurt the bodies to save the souls, even of his dearest children. 4th, Satan, that intendeth hurt, is oft God’s instrument to do us good. 5th, Bodily pains are oft the messengers of Satan, and yet of God.”
The messenger of Satan - Among the Hebrews it was customary to attribute severe and painful diseases to Satan; compare Job 2:6-7; compare note on Luke 13:16. In the time of the Saviour malignant spirits are known to have taken possession of the body in numerous cases, and to have produced painful bodily diseases, and Paul here says that Satan was permitted to bring this calamity on him.
Messenger of Satan (ἄγγελος Σατᾶν)
The torment is thus personified. Messenger is the word commonly rendered angel in the New Testament, though sometimes used of human messengers, as Luke 7:24, Luke 7:27; Luke 9:52; James 2:25; see also on the angels of the churches, Revelation 1:20. Messenger and Satan are not to be taken in apposition - a messenger who was Satan - because Satan is never called ἄγγελος in the New Testament. Messenger is figurative, in the sense of agent. Satan is conceived in the New Testament as the originator of bodily evil. Thus, in the gospel narrative, demoniac possession is often accompanied with some form of disease. Compare Luke 13:16; Acts 10:38, and see on 1 Corinthians 5:5.