He's quitting because chess.com was unreasonable soft on Niemann earlier?
Chess.com on Niemann ban

No real evidence of Hans cheating. And it actually appears that he didn't.
The Great Magnus ruined the round robin tournament. Magnus deserves more criticism than Hans at the point. If Hans was cheating that is no reason for Magnus to not play the games with the remaining players. Round robin tournament format means that if one player drops out it totally screws up the tournament. Magnus leaves without explanation after playing subpar. Subpar is not MY analysis but those more advanced than I. Sounds like Magnus is acting like a sore loser.

Hans' results at the start of the Sinquefield tournament are consistent with cheating. His results after round 3 of the tournament are consistent with him being a weaker player than the one who played the first three games. I suspect there is not sufficient evidence to prove cheating in this tournament - chess.com often requires 50 games of cheating to detect a less obvious cheater.
However, Hans past record leads to it being most likely that he cheated at Sinquefield. It's like if an athlete gets caught twice for doping, then has some extraordinary pattern of getting much better results in events where it is possible to get away with doping, then he breaks a world record, you can be rather sure he doped.

What you say may be true. I do not know. These GM's play like computers compared to me. I do know that analysis made by people I trust contradict what you have said here.
Regardless of cheating or not which I do not know or concede Magnus ruined the tournament by exiting. If he thinks there was cheating... he should says so. My post on this subject are not so much to defend Hans. I hate cheaters with a passion. And he has cheated in the past. But he is a very very good chess player and mere accusations without hard evidence to back it up are wrong. It is wrong to bash a good man without some proof. It is likewise wrong to bash Hans without any proof.
And like I said, others have contradicted that cheat pattern of his games that you have made.

Hans' results at the start of the Sinquefield tournament are consistent with cheating. His results after round 3 of the tournament are consistent with him being a weaker player than the one who played the first three games. I suspect there is not sufficient evidence to prove cheating in this tournament - chess.com often requires 50 games of cheating to detect a less obvious cheater.
However, Hans past record leads to it being most likely that he cheated at Sinquefield. It's like if an athlete gets caught twice for doping, then has some extraordinary pattern of getting much better results in events where it is possible to get away with doping, then he breaks a world record, you can be rather sure he doped.
Surely he has enough otb games in general to make an analysis on how likely Hans has cheated otb in the past? That would be a big step in the investigation. I've seen some headlines that some of his games in the past have been suspicious but is there enough collective data on his games that we could make a conclusion that he has likely cheated otb?

It is quite difficult to prove a strong master player is cheating, especially if they do so intermittently, and whether it can be done clearly depends on the subtle detail of the analysis performed.
That being said, one selection criterion helps - Niemann's games with a live relay are much stronger than his games without live relay (even based on the results alone) and while the totality of his OTB play in recent years is suspicious, that with live relay is likely way more so. Note that cheat detection is about the statistical relationship between the moves played and engine evaluations. (The detailed analysis used by chess.com is of course secret, for obvious reasons, and this was sufficient to prove Niemann cheated on multiple occasions. To get caught, Niemann was a player who was systematically using an engine to assist his play, not merely occasionally referring to one. That he did this at least twice over 4 years says everything about his personal attitude to cheating).
I agree that most of Niemann's talk about his games is suspicious. It is a combination of weird comments about his opponents, apparent lack of understanding of what is going on his games, avoidance of doing analysis consistent with the quality of play and implausible excuses for suspicious characteristics of his play.

You're not owed an apology at all.
Collectively I believe that we are.
Most of the "chess community" are just passive consumers of free content, I don't see how they're owed an apology for an incident that hasn't even had a complete explanation yet. If Magnus (or anyone) wants to quit tournaments without explanation that's up to them. I know in the age of social media, 24-hour news cycles and short attention spans people demand immediate answers to everything, but that's not the way everything works.
I don't care. Obviously, people cheat. Obviously, people who are accused of cheating haven't cheated. It presumably happens at all levels ...... both sides of it. People cheat at football. People do all sorts and others who are accused of it don't.
It will probably sort itself out, one way or another but once you get a reputation for dishonesty, it tends to stick.
Amen. It can often take MANY years for someone to dig themselves out of that hole they put themselves in. Which is why I say someday, maybe 30 years from now we can say Hans used to be a cheater. But as of today, he IS a cheater.

Clearly the standard for proving someone cheated is beating MC with black. So warning to all MC opponents don't try to win with black.
I know, I know, Hans cheated twice that we know about when he was 12 and a once a few years later. I realize that suspecting Hans cheated is different than someone else is the same spot.
But still the only evidence present is that some people say that it appears he cheated and many others have said that is not the case. I would think that people would not want to hop on the bandwagon that Hans cheated when the evidence is so weak. Cheating as a child is not proof of cheating as an adult.
I bet I hate cheaters more than almost everyone, but I don't want to be part of accusing someone and trashing them in public and then find out later I was wrong and he wasn't cheating at all.
If that is the case you would be part of tainting and soiling the greatest moment in that persons life. Can you imagine beating MC with black (or white). That is like winning the superbowl. And having that tainted forever with assumptions and negative news.
Contrast "Bright up and coming star defeats MC with Black". With "Magnus loses to 19 year old, cheating suspected."
Do you want to put those headlines in your scrap book.
Just saying I will not be party to accusing someone that just accomplished a huge victory of cheating with out some real proof.

No one has ever been banned online for a game they played OTB.
Until now . Money talks.

No one has ever been banned online for a game they played OTB.
Until now . Money talks.
So do idiots, unfortunately.

Cheating as a child is not proof of cheating as an adult.
Not a single person has claimed Hans cheating in the past is "proof" he has cheated over the last 3 years. But he has cheated at 12, promised never to do it again, cheated at 16, promised never to do it again, made the pathetic excuse that he cheated so he could play stronger players - presumably it never occurred to him that you can do that by beating weaker players without cheating! - and given what has been revealed to be a wildly inaccurate description to the world of the extent of his cheating, and is now 19.
Who would doubt him?
Then there is the very interesting fact that Hans's OTB play has been reported to be unambiguously stronger when there is a factor that helps to enable cheating. This includes the first three games of Sinquefield 2022.
Hmm.

Clearly the standard for proving someone cheated is beating MC with black.
Clearly post hoc ergo propter hoc.
Clearly the most basic logical fallacies have to be rediscovered over and over.
And over, and over...

Then there is the very interesting fact that Hans's OTB play has been reported to be unambiguously stronger when there is a factor that helps to enable cheating. This includes the first three games of Sinquefield 2022.
What do you mean by this?

Then there is the very interesting fact that Hans's OTB play has been reported to be unambiguously stronger when there is a factor that helps to enable cheating. This includes the first three games of Sinquefield 2022.
What do you mean by this?
The only ambiguous part of his post is that "there is a factor" = "the position of his games is broadcast to the public via a DGT board." The obvious implication being that an accomplice then analyzes the position with an engine, and covertly signals Hans some kind of information.
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And it's true that in tournaments with DGT boards his performance rating was higher, and in St Louis his performance was lower after they implemented a delayed broadcast.
If this were the only evidence there'd still be some room for doubt, but add to it his online cheating, lying about cheating, strange post game interviews, and Carlsen's odd behavior and there is a lot of reason to believe he has cheated OTB in a non-zero number of games.
While of course everyone has the right to make foolish decisions to spite themselves, bear in mind that Niemann cheated more than once on chess.com (including by his own admission, if you have any doubt), then lied about the extent of his cheating. To die on the hill of protecting his honour is daft. Especially since the evidence of OTB cheating is reported to be convincing, making it almost certain in the context of the other facts.
Perhaps by cancelling his membership he is not in the business of defending another player's honour, but making a statement to the site to the point of 'treat all players equally and fairly'.