The claim that our perception is subjective means that it can never learn anything about the objective world. Because every conclusion would also be subjective.

You reminded me of a saying of Einstein’s, but I won’t repeat it here. If you repeat the same sentence again, do you think that makes it stop being a tautology? I’m astonished!

So in practice, the Rabbi accepts that nothing can be learned about the external world, such that the truth is that there is no one truth. That’s it—the modern postmodernism has won??

Wow, what an Olympic leap. You asked whether A->A, and I answered that of course it does, since that is a tautology. And now you’ve put into my mouth that I think A. Wonderful are the ways of your logic.

So the Rabbi doesn’t accept the premise at all that our thought is subjective? As you wrote, “And now you’ve put into my mouth that I think A.” If indeed not, why?
And if the Rabbi does accept it—then how do you think our thought can say something true about the external world in an objective way? (After all, objective is not subjective.)
And if it really cannot say anything, then how are we able to claim that some statement of ours about the external world is true or false, when there is an unbridgeable gap between us and the reality around us? Doesn’t that mean that postmodernism has definitively won?

No. It is not subjective in the misleading sense, but in the translating sense. A translation of reality into the subjective language of my consciousness (an electromagnetic wave is translated into color, etc.).

But if we have never encountered the thing in itself, then there is no reason to assume that the translation is correct.
And therefore all of our perception is subjective and says nothing about the world as it is in itself. That is, for example, why sensations and experiences are so significant in many places, even against facts.

There is no need to encounter the thing in itself, because it is impossible to encounter it. The encounter with it is the creation of its image in our consciousness (the phenomenon). And not like those mistaken people who think that Kant is talking about limitations in our cognition. He is not. There is no limitation here at all, only a description of the mode of perception. The thing itself has no color, only some kind of structure that produces color in us. Therefore, our perceiving it in terms of color is neither a limitation nor a mistake. That is how its structure is expressed in our subjective language.
Anything beyond that is mere skepticism, and there is no point in dealing with it. If you are a skeptic, nothing will get you out of that. And if you are not, then no arguments are needed.