In the commentary on the Mishnah by Maimonides, in the introduction to the chapter Helek, laws are brought that are laws given to Moses at Sinai, and there are two oddities there. A. “The cantor reads with the children by candlelight,” which is altogether a leniency within an existing law that is rabbinic. B. Maimonides writes there that no dispute ever arose regarding a law given to Moses at Sinai, but he gives as an example the area of a sukkah, which is in dispute among the tannaim in the Mishnah in tractate Sukkah.

Also, the law given to Moses at Sinai of ten saplings is a detailed element within the existing law (which is not itself a law given to Moses at Sinai) of the added prohibition before the Sabbatical year. It isn’t clear that this is from the Torah and not straightforward at all. If I remember correctly, somewhere — maybe in Moed Katan — the Talmud discusses whether one can prove that this added Sabbatical prohibition is Torah-level from that law given to Moses at Sinai.
And also see in tractate Pesachim, in the Talmud on the tenth chapter, the law given to Moses at Sinai regarding “pairs” — which is strange.
It seems likely to me that for Maimonides, “law given to Moses at Sinai” means an agreed-upon law.

He writes explicitly that these are laws transmitted from Sinai. But beyond that, what do you gain from that definition? After all, the area of a sukkah is not agreed upon, so why would that be a law given to Moses at Sinai according to your approach? And as is well known, the Chavot Ya’ir already addressed this in his famous responsum (192, if I recall correctly), that there are many laws given to Moses at Sinai about which disputes did arise, contrary to Maimonides’ words.

A. He writes it, but hints at it…
B. After they disputed it, it was ruled on and settled.

With that kind of interpretive freedom, I could suggest that according to Maimonides, a law given to Moses at Sinai is anything said at latitude 225 and northward between 7 and 11 a.m. There’s no substance to that.
If everything that was ruled on is a law given to Moses at Sinai, then there are thousands of such laws with not the slightest hint that anyone relates to them that way.
According to Maimonides in several places, in the case of doubt a law given to Moses at Sinai is treated leniently, and its status is like that of rabbinic law.
He says explicitly that it was given at Sinai, and therefore no dispute arose about it.
And there are many more arguments besides. Really, this is a waste of time.

If it weren’t such a waste of time, please explain the rabbinic laws included there.
In general, the whole technique of transmitting certain laws orally, where some have textual hints and some do not, is puzzling.
And another fundamental question: fine, the Torah and its interpretation derived from it through the thirteen hermeneutical principles are binding. But statements of Moses — why are they binding? If because of his prophecy — “it is not in Heaven.”

That isn’t connected to our discussion. Indeed, Maimonides’ words there require further analysis. The same is true of what he says in the ninth root, where he derives a Torah-level prohibition against eating before prayer from “Do not eat over the blood.” But in any case, that has no connection to our discussion here, for the reasons mentioned above.

I didn’t understand what is puzzling about transmitting laws, some of which have a hint in the text and others not? Maimonides himself (in the second root and in the introduction to his commentary on the Mishnah) distinguishes: the former are Torah-level and the latter are rabbinic. In my book Ruach HaMishpat I explained this well.

These are not statements of Moses, but things he received orally from the Holy One, blessed be He. Beyond that, Moses’ statements are binding because he had the status of a Sanhedrin. And as is known, the medieval authorities dispute whether his enactments have the status of Torah law, although in my opinion that is untenable.

Despite the emphatic statements, it’s worth noting:
A. Indeed, his language is fairly clear: a law given to Moses at Sinai was said to Moses.
B. Yet almost immediately there are two cases where a law given to Moses at Sinai revolves around a rabbinic enactment (“the cantor reads” and “Ammon and Moab tithe in the seventh year”). It’s very forced to dismiss this with a shrug.
C. Maimonides sometimes used a method of hidden statements (he explains this in the introduction to Guide for the Perplexed).
D. In all laws not explicitly written in the Torah, the Sanhedrin has interpretive freedom. When they say about something that it is a law given to Moses at Sinai, the intention is that in the Gemara’s view (whose authority is that of a Sanhedrin… and that itself requires analysis), here there is no interpretive freedom. And furthermore — even if there is a minority opinion and so-and-so is worthy of being relied upon in pressing circumstances and so on — here, no.
E. According to your view, that these laws said to Moses have the authority of the Sanhedrin, can a later Sanhedrin disagree with them? At least regarding laws where one cannot say they are decrees and protective fences — because then who is greater for us than the Sanhedrin of Moses?

B-C. If you’re going in the direction of esotericism, then there’s no point discussing Maimonides’ position at all, because everything he says won’t prove anything.
The shrugging isn’t about me. That’s a difficulty on the Gemara itself, and the medieval authorities already noted it. (“Ammon and Moab” as a law given to Moses at Sinai is explicit in the Talmud in Hagigah.) So I wouldn’t infer anything from there. Tosafot writes about a Mishnah in Parah, where the death penalty is stated regarding a rabbinic law, that this is merely language of reinforcement. But that is the exception that proves the rule: a law given to Moses at Sinai, like liability for the death penalty, is usually meant literally, aside from places where it is said metaphorically for emphasis.
And I already mentioned the Chavot Ya’ir, who brought a great many examples where Maimonides’ words do not hold up — not only these two. And in most of the examples, a dispute did arise, which is itself his question on Maimonides. So if anything, if you rely on examples, the conclusion is the opposite of yours: a dispute can arise even regarding a law given to Moses at Sinai.
D. Why is there no interpretive freedom? Because the earlier Sanhedrin decided it? Then the later one disagrees with it on that very point. There’s no sense or flavor to that.
E. Certainly not. According to Maimonides, no dispute ever arose about what was said to Moses. Just like what is written in the Torah. By the way, according to Maimonides’ own approach, in several places a law given to Moses at Sinai is treated as rabbinic law in terms of its halakhic status. There are contradictions here, but they can be resolved, and this is not the place.