Dispute over the Rambam

Hello, Rabbi. I understood from your honor that in his opinion some of the laws and even the Torah itself were not received at Mount Sinai, but rather during the history of the Jewish people, and yet the laws have binding force even if they were supposedly not given at Mount Sinai. But Maimonides listed 13 principles that must be believed with complete faith that the Torah in its entirety was given at Mount Sinai, and I have not found anyone who disagrees with him, so apparently there is a halakhic obligation here that must be believed in even if it is difficult to agree with him, just as you claim that the laws of the arbitrator must be observed even if in your opinion this is not a task. And if we say that there is no halakhic obligation to believe in the 13 principles because there is faith and there is halakhic law, what about the halakhic implications regarding a person who does not believe in these principles? After all, such a person is disqualified from testifying, his flesh is rotten, he has no share in the world to come, these are clear halakhic implications.. To me, this seems a bit like a contradiction. What is his opinion?