Meaning of the commandments of an infidel

Thanks for the clarity.
” There are no sanctions for those who truly believe what they believe, even if they are considered by you to be a ”
That is to say? Did the Sages impose ‘sin’ sanctions only on the criminal infidel?

Or is it that he is a ‘sin’ towards other people, and not towards himself, because according to his understanding that this is the truth, there can be no sanctions for the truth? According to this assumption:
Even if according to the Sages I do not join the minyan, if according to my system I can – I have no reason to ‘fail’ others because I know that I am right; just as I would be allowed to feed a person a piece of meat that 100 witnesses testified was milk, if I know that it is fat. (Or am I wrong in this case too?)

Of course not. Anyone who truly believes in something is a forced believer (in his beliefs), and it is not appropriate to impose sanctions on him. The sages simply assumed that it is possible for a person not to believe because of a crime/instinct. They did not meet people who really came to other conclusions, at least not in a reasonable number. Nowadays, this is the usual situation.
The question of who is a “sex” is not really interesting. A person determines his own positions according to what he thinks and not according to the title, believer, convert, sex, infidel, Epicurus, and so on. The attitude of others towards him does not really matter as long as he believes what he believes. All these discussions are meaningless and there is no point in engaging in them.
There is a moral (and also halakhic) problem in stumbling people into what they believe is forbidden, even if you think it is permitted. See column 503 and in the articles here:
https://mikyab.net/%D7%9B%D7%AA%D7%91%D7%99%D7%9D/%D7%9E%D7%90%D7%9E%D7%A8%D7%99%D7%9D/%D7%9E%D7%97%D7%99%D7%A8%D7%94-%D7%A9%D7%9C-%D7%94%D7%A1%D7%95%D7%91%D7%9C%D7%A0%D7%95%D7%AA

How do you know that they once did not truly reach other conclusions and renounced only because of crime and instinct? Isn't it possible that the sects that seceded during the Second Temple period truly believed what they believed?

Two reasons: 1. It is well known that the phenomenon of ideological apostasy (secularism) is new. At least as a phenomenon. In the time of Chazal, a convert was made to anger and appetize. There was no ideological convert (at least as a phenomenon). 2. If Chazal had seen an ideological apostate before their eyes, then it is clear that they would not have imposed sanctions on him. He is completely apostate. But they do see this as an offense that requires a sanction, and therefore I conclude that their apostates were probably not apostates. See column 568, which appeared just now.

By the way, even if there were ideological heretics, Chazal's view was that they were not. The burden of proof is on the one who claims to be one. This is seen in countless contexts.

Are you denying that during the time of Chazal, there were many sects, each with their own ideology, and not just heretics?

No. I deny that the sages perceived them as ideological heretics (erroneous in their judgment). They saw them as sinners because of their instinct: converted to anger or appetite. And if there were anyone who was not, then there really would not have been sanctions imposed on him.

How can one not believe because of a crime or an instinct? At most, one can not carry out actions or behaviors that stem from belief. But if a person thinks that a certain claim is true, no instinct can move him to do so.
It's like a person who thinks that from a health perspective he is forbidden to eat meat. He may be tempted and eat meat, but he clearly will not think that from a health perspective he is allowed to eat meat.
Or a person who breaks the law because, say, greed. This does not mean that he thinks there is no law here.
If a person could choose what to believe, then people would live in an imaginary world and lose touch with reality. Because it is always easy to imagine that you are in a perfect world. Believing that the world you created is reality is impossible. Perhaps under the influence of drugs.

You might be surprised, but it is definitely possible. A convert to anger and appetite can also be in beliefs. He puts himself into a certain perception because of an instinct, and then lives within it. Actions that are every day. A person finds justifications for the actions he does, even though deep down he knows that there is no justification here. I have argued this in many places, and you can search here on the site for my discussion of the Hindi parable.
There is an interesting epistle by Rabbi Schach about “stealing the mind of his neighbor” (as I think was said about Cain). A person whose hat flies outside the boundaries of Shabbat or the Iruv, he convinces himself that God does not see and quickly goes out and comes back. People convince themselves of many things.

If deep down he knows that there is no justification here, then where is the lack of faith here? He believes but suppresses the faith because of feelings of guilt.

And if in the end he really believes because of instinct, then it turns out that a person can choose to believe, and then how is it possible to rape a person who does not believe out of ideology. After all, he can convince himself to believe and change his ideology, but he chooses not to.

Likewise, if a person can choose what to believe, then he can convince himself to believe in nonsense because life is difficult and in fact lose touch with reality. Like believing that he will never die, that he is a billionaire, that he is Napoleon. But a healthy person would not believe these things. That doesn't work for me.

Following A's question,
Why would he go all this strange way of convincing himself that there is no God and that he is a heretic, and along the way also live a more difficult life without faith, and not convince himself that the prohibition he wants to transgress does not exist, or that it can be circumvented in a certain way, as many traditional and even religious people do?
Yesterday I read about a traditional believer who lights Shabbat candles and prays but does not observe the commandments. If she can convince herself that it is okay, why go all the way to complete apostasy?

Also, if it is clear to him that his apostasy is not true, does he not believe in denial?

People are complicated creatures. There are passions, influences, etc. You are asking Rav Ashi's question about King Manasseh.