Roots and Branches – The Second Root

Maimonides defines everything learned from the 13 Midots as the words of the scribes. The rabbi went on to explain his words.
Does the Anfim say that they doubt the severity or the tone? Someone who was satisfied if he mentioned the Exodus at night, seemingly repeats and mentions, and the mention of the Exodus at night is learned from the plural, which is an Anfim. What is the fundamental difference between such a doubt and doubting if he recited the Shema without repeating the opinion of the one who believes it is from the rabbis?
Can we connect the words of the Maimonides with the words of the Rabbi of the Covenant, who said that the oath and standing at Mount Sinai are only said about what is actually written in the Torah?