logic

Good evening.
The Rabbi said in the past (‘Ma’aseh B’70’ time 8:27. ‘Rosh Rosh’ time 1:20:18) that nothing is certain, except for this claim.
The Rabbi said to the AHM (debate with Yaron Yadan, time 1:11:28) that nothing is certain, including this claim.
I would love to understand the conclusion.
I’ll focus. I tend to stick with the first sentence. Because,

1. The claim that “there is content/truth” is a certain claim. Since I am unable to claim something that escapes assertion (-truth). (To claim that ” perhaps there is no truth” is also an assertion)
2. I approach classifying content into the framework of ‘certainty’, according to 1. (For example, the claim that “positive and negative are neutral” is a certain claim, since I fail to claim something (for example, the claim that “positive and negative are not neutral” neutralizes the claim that “they are neutral”) that escapes neutralization).
3. When I approach to investigate the content of X (in order to classify), and I try to deny it, and the attempt to deny does not fall into the above-mentioned fallacy, then I do not classify it within the framework of ‘certainty’.
4. However, the claim that he is not within the framework is a certain claim (because I am ‘certain’ what the framework is).

Now, to claim that “this last claim is also uncertain,” meaning that “it is possible that X is indeed a certain content,” is in fact to claim (/determine (with certainty)) that it is uncertain. (That is, at the time and stage of the claim that X is a heresy in its content, it does not fall into the above-mentioned fallacy.)
Clarification. I ask:

1. Do you actually mean, in your words (in the first sentence), “except for this claim,” to claim that the sentence “there is truth” is a certain content? (That is, that there is something stable). (Clarification regarding my argument (that “there is certainty/truth”): Apparently, a skeptic would claim that “the fact that there is no truth is also an assertion does not mean that there is truth, and so on, God forbid, etc.” and so on, I do not understand sentences of this kind.)
2. What is your conclusion about these words, and why?

Thank you in advance.