“You can follow the halakhic system and method of Rambam to disagree with Rambam on a specific issue”
For Maimonides, he acknowledged that the authority that he had to write the Mishneh Torah wasn’t from himself, it was really from the Talmud; in that, according to the language of the Rambam, you follow מי שהדעת נוטה – whomever convinces you the best.
By what does it mean the best? Having the best read of the Talmudic law; such that, if you have a better read of the Gemara than the Rambam, then you can disagree with the Rambam. Or, to put it another way, you can follow the halakhic system and method of Rambam to disagree with Rambam on a specific issue; meaning Rambam can write something is Jewish law – you can go back to the Gemara and say “Excuse me, Mr. Rambam, that’s not what the Gemara says.” or “We have a better text.” And, that way, even if people say, “Oh, aren’t you arguing with the Rambam?”, the answer is yes and no: you’re following the method, which is a lot more important than the details of the person, the individual.
So, Maimonides derived whatever authority he had only based on the Talmud, itself.
Rabbi Josh Yuter, “Halakhic Process 27 – Summary and Conclusions”, Yutopia Podcast #123 (10 November 2013).