Regarding a food that contains dairy

I thought that a distinction should be made between the Haftsa of a thing that has a permissible nature and the prohibitions of the gabra that have a permissible nature. For example, leaven on Passover or Tevel is a Haftsa prohibition that has a permissible nature, but dairy food does not have a Haftsa prohibition, but only a prohibition of the gabra, and therefore the law “until you eat it with a prohibition, eat it with permission” does not apply to it. By the way,

I saw a source on WikiShiva regarding an oath about a food item (= a prohibition of the gabra) that says this:
An oath – such as swearing about something that we will not eat – The Rishonim wrote that it is something that is permissible (this is what the Rambam says in Nedarim 5:14-15; Ritva Shavuot 4:1; this is what the Migdal Oz says in Ibid. 15, and Ritva 7:16; Peri Maggid, Opening of Passover 2:16), which is a mitzvah to be asked about (Ritva 1:1); and some of the Aharonim wrote that an oath is not something that is permissible, that there is no mitzvah to be asked about the oath, and on the contrary, no one is asked about the oath except by force (see the article on oath), and that whoever swears not to eat a certain thing and the matter is mixed with others is invalid in the majority (Beit Yaakov 11; Teshuva Ma’ahabah 124; Fathei Teshuva 4:16, by their names).

That is, even according to some of the Aharonim, an oath (and perhaps also all the prohibitions of the Creator) is not something that is permissible.

And I found something similar on Wikisheva regarding nuns, which is not something that is permissible. For example, grape wine mixed with fig wine, and the nun wants to drink it. Although it is possible to ask a sage, it is not considered permissible, because the question to the sage is about nuns themselves (who will abolish nuns) and not about forbidden things (such as drinking wine), and only when the sage uproots nuns - the prohibition of drinking wine is abolished anyway, therefore it is not considered permissible (deciphering the rules of the Torah and the commandments, 3:1, 4).

What do you think?

The prohibition of meat in milk is a Haftsa prohibition. It is true that the obligation to wait between meat and milk is from the rabbis and perhaps only for men (although I am not sure about this either).
Incidentally, in monasticism, I think that this is a slightly different explanation. There, it is about permission and not about the prohibition. Permission is not for a thing but for a person.
In the case of an oath, the explanation seems puzzling to me. Especially if you say that it is a prohibition for men. But since there is no mitzvah to be asked, then there is also no mitzvah to be asked in a vow, and it is made clear in Tractate Nedarim that a vow is something that has a permit.

Furthermore, the explanation for the division between the prohibitions of the Creator and the Law of Hastza seems to me more about cancellation. But with regard to the laws of spikut, I see no difference. Until you eat it under prohibition, you eat it under permission.

You wrote about nuns that the permission is not for a thing but for a person. This is exactly what I was trying to say, that in the prohibitions of Gavra, the permission is not for a thing (for a desire) but for a person (for a person). Therefore, in the prohibitions of Gavra, the law of a thing that has a permit does not apply (as in nuns), and therefore I am trying to argue that the sufficiency of the prohibition of Gavra that has a permit from the rabbis is as much as the rabbis doubt about the koll (as opposed to doubting the prohibitions of Gavra that have a permit). Regarding dairy food, in the body of the food there is no prohibition as long as it has not mixed with meat, only after you eat it does the prohibition actually apply (let's say it mixes in the stomach) and therefore it suffices for the koll (because it is the law of the rabbis).

As I added, regarding the doubt of the rabbinic rabbinate, I do not at all understand the explanation for dividing between gabra and hafza. Perhaps this can be said about cancellation.
What I meant to say about nuns is that you brought up two formulations: the prohibition on the thing or on the person. The permission is on the thing or on the person. For example, in the vow, the prohibition is on the thing, but if there is a permission for the person, this does not permit the thing per se. But this is just a side note.
And regarding eating dairy food, that is what I said. If it mixes in the stomach, or alternatively if the milk becomes a hafza prohibition if you ate meat, then this is also a hafza prohibition.

The explanation for the division, in my opinion, stems from the source in the Gemara for the law of a thing that is permissible. We learn this law from an egg that was born on a day of rest. In other words, I am trying to argue that the entire law of De'Shal'am pertains only to objects of prohibition, such as an egg that was born on a Yom Tov, leaven on Passover, immersion, etc., but does not pertain to prohibitions that are not objects of prohibition, such as wine for a Nazirite, or just any edible item on a fast day. For example, if a person wants to eat on the night of Tisha B'Av between the sunsets, there is apparently a doubt here about the rabbinic prohibition (= to drink), but on the other hand it is a prohibition that is permissible (when the stars come out, it will be permissible), and yet I am trying to argue that it would be permissible to relax this prohibition without waiting for the stars to come out, because all the laws of "a thing that is permissible" pertain only to objects of prohibition, and not to divine prohibitions such as the obligation to fast on Tisha B'Av.

Sometimes halakhic formalism does work this way. But the idea that something is permissible exists in both the Haftza and the Gabra prohibitions: Until you permit it, there is doubt about the prohibition, wait a little, and it will be eaten with complete permission.

If a person ate meat and now, an hour after eating the meat, wants to eat something fermented that was cooked in a milk pot. What is the ruling? And the taste?

http://www.yeshiva.org.il/midrash/19282

Following this question, does the rule that one should be stricter in cases of doubt about something that is permissible, apply only to doubts in reality, or also to legal sufficiency? For example, there is disagreement among the poskim as to whether one should wait a certain amount of time after eating cheese before eating meat becomes permissible. Would it be correct to follow the rule that the rabbis doubted until the kollah, or should one be stricter precisely because of the rule that doubted in the shi'lâm to the khumrah?

Apparently, in a doubt in law, there is a side to be stricter even without a shi'l, at least in a doubt of darbawta, because here perhaps both sides are right (them and the others). In any case, at least in shi'l, it seems to me that one should be stricter in this too, for the same reason (until you eat what is forbidden, we eat what is permitted).

If I understand you correctly, in any doubt about the law of the rabbis, one must be stricter? And the poskim usually use the common rule of doubting the rabbis' voice even regarding halachic disputes in the law of the rabbis, don't they?

No. I wrote that there is such a side. For example, regarding the question of Sfiqa, some wrote that in doubt in law there is no permission to leniently grant it. See for example here:
http://www.yeshiva.org.il/wiki/index.php?title=%D7%A1%D7%A4%D7%99%D7%A7%D7%90_%D7%93%D7%93%D7%99%D7%A0%D7%90

It is precisely from the source you cited that I understood the opposite. It says there:
“In the spicah, the rabbis also lenient in the dispute of the poskim (Mishnah Berura 26-37).”
And in addition it says there:
“Spicah spicah – They do not say spicah spicah in the dispute of the poskim (Shab Shematata 1-23 in the name of the Mahariv”l).”
That is, they mean that it seems to me that there is no difference between a spicah spicah and a regular doubt in the dispute of the poskim. From this it follows that there is doubt in a law in the Torah and in the Torah and in the Torah (there is no difference between one doubt and a spicah spicah). And the same thing also in the rabbis, let's say there is a dispute among the poskim regarding law A. And even among the faction of poskim who lenient in law A, there is a dispute among themselves, whether regarding law B, which branches from it, should be lenient or stricter. If both laws A and B are rabbinical, then even if there is a spiqa doubt regarding law B whether it is permissible to relax it – The first doubt is whether the strict faction in A is right (and then B should also be tightened), and the second doubt is that even if we say that the lenient faction in A is right, whether the strict faction in B is right, we should still relax law B because of the rabbinical doubt. Did I understand correctly?

Incidentally, I noticed that it says something else there, contrary to what you said above regarding my original question:
“A thing that is permissible is not prohibited by spiqa dedina, but only by doubt in reality (Rek”a Berakhot 2. (end of D”e there and Mayai) brings a par”h regarding spiqa rabbinical, and adds from his own knowledge also regarding the spiqa doubt).”

Indeed. In doubt, the rabbis also make light of the dispute between the poskim, and that is what I wrote. And regarding the Ss, it is not a question of two spikits of the poskim, but rather a doubt upon a doubt in the poskim. In the Dauraita, they are stricter about this because the first doubt is not considered a real doubt (both sides of it are true), and that is what I wrote.

Regarding Dashilam, I do not remember this, but perhaps Rek’a writes this. It seems to me that this is not the case. Perhaps the same reasoning applies here that in doubt in the poskim, both sides are correct, and therefore one can rely on the mitigating side, and it is not considered that you are now eating in a forbidden state (which is the reasoning for not eating and postponing eating to the permissible level).