IMO people over complicate Mary Sue. For me there are 3 fundamental things you need.
1.) Must be beloved by everyone important (no ones cares if ACKTUALLY NOT MARY SUE! THE JANITOR IN THE BACKGROUND SECRETLY HATES THEM PER WORD OF GOD!) for no explicable reason, and must maintain this status regardless of if it makes any sense.
2.) Must be better than everyone at [insert thing they're good at]. Again no explanation or token non-explanation for this.
3.) Must never personally lose a engagement. They can suffer large scale set backs as part of a group but in a one on one engagement they will always come out on top. I'm talking even if they definitively lose, they somehow are actually now ahead of their opponent, even if it is in the most bullshit nonsense way.
Following these criteria we have Pure Mary Sues
John Kramer (Jigsaw)
Rey Palpatine
Wesley Crusher
Abeloth is a villain sue
Wakanda as a nation
Conditional Mary Sues
Wolverine & Batman under bad writers (This is kind of cheating because you can blame bad writers for anything but these two get it consistently)
Billy Butcher from The Boys, in the same vein many would argue Garth Ennis' Punisher (I would argue against at least Punisher due to almost everyone in universe hating both. It's undeniable though that the universe as a whole schemes to constantly validate these guys)
Pre MtmtE Drift from OG IDW Transformers
Ultra Marines & Grey Knights under the pen of The Spiritual Liege
Post Rebels Ahsoka Tano
Basically what I'm saying is pure consistent no matter what Sue's are a rare breed and require serious fucking delusion or purposeful fuckery. Usually Sue's spring from incompetent writers on specific projects, arcs, being forced to write characters they don't know, etc...