They are about the same event. 11Thess.2 is about the end of days. Paul tells us that Christ will not come back until after Satan.
2:3 Let no man deceive you by any means: for that day shall not come, except there come a falling away first, and that man of sin be revealed, the son of perdition.
We know the son of perdition is Satan and that is who vs. 7 speaks of. He is held but will be released at the 6th trump, 6th vial and 6th seal (666 Mark of the beast) by Michael. We know it is Michael because Rev. 12:7 tells us that.
As to the identity of the one who restrains, the Church (and readers of the religion forum know that by that I mean what is commonly called the (Eastern) Orthodox Church, but which is properly the One, Holy Catholic and Apostolic Church, claims to the title ‘Catholic’ by the Latins notwithstanding) has always identified the one who restrains with the Christian Emperor, who was ‘set aside’ in 1917 with the abdication of the last Tsar.
It isn't the church as scripture tells us who restrains Satan and that is Michael.
You misread Paul’s second letter to the Thesselonians if you equate the one who restrains the mystery of lawlessness with Michael as the adversary of Satan.
The one who restrains is taken away, while Michael prevails over Satan and his angels.
Nor is the “man of sin, the son of perdition,” Satan, but Antichrist, who will be a man, (note, *man* of sin, not spirit of sin, not angel of sin, *man* of sin) who seeks to set himself in place of Christ.
If you doubt the Church’s interpretation of St. Paul’s reference to ‘the one who restrains’, consider the difference between the state of the world prior to the abdication of the last Tsar, (and the fall of the Kaiser, the last Western claimant to the old Roman Imperial title) and the state since.
Circa 1900, Europe was full of pious Christians of one type or another, virtues like chastity and self-sacrifice were held in high esteem, Christian piety was stronger in America than since, Christian missionaries were free to preach throughout all areas under American or European influence, which meant the entire globe, save the Ottoman Empire, where the Orthodox, Copts, Jacobites, Armenians, and Nestorians were tolerated minorities, and the already-Christianized Latin America.
Fast forward to the 1920’s and 30’s: the Church in Russia is persecuted, the collapse of the Ottoman Empire leaves in its place in the original Christian heartland, regimes even less tolerant of Christianity, cracks in the embrace of traditional virtues are seen throughout the West, from the flappers to the resolution of the Oxford Union, ‘this house will not fight for King and Country’, evil, anti-Christian ideologies compete for dominance. By the 1950’s atheistic communism, which is most assuredly lawless, has closed of much of the world to Christian preaching. By the turn of the 21st century, only 4% of Western Europe self-identifies as Christian (the number being better in the Christian East, where it never dipped below 40% in Russia, even at the height of the Bolshevik persecution, and stays at 80% in Romania, and over 90% in Greece), abortion is accepted and homoeroticism tolerated or even promoted in nominally Christian societies, and Islam, the original Antichrist (being the first religious movement to create itself in opposition to the Gospel), is once again fighting against Christians (in the Balkans aided by the nominal Christians of the West).
The mystery of lawlessness works, and manifestly so, since the one who restrains has been set aside.