On this matter, in my opinion the Zohar and Kabbalah mainly deal with divinity and its representations (sefirot, configurations, etc.),
not with the Creator Himself — “No thought can grasp You at all.”

If you look at it that way (and there’s no reason not to), I don’t see any reason to be concerned about Kabbalah.

But they speak of unifying the name YHVH, and the name YHVH is His very essence, blessed be He — how can you unify Him??

It’s not as though it is His essence itself, but rather it describes His essence.

The name Y-H-V-H does not describe His essence, blessed be He, but rather the Name Havayah. Even the Infinite Light is not His essence and being, blessed be He. Again, it depends on the context. There are also those who say the name Elohim, or who say “God” — it seems they mean His essence and being. And also someone who says “the Lord.” Broadly speaking, from what I understood from people who studied books of Kabbalah and Hasidism, His essence and being have no definition, and that too requires deep study in its own right. In any case, all the other names express a limited divine light: the name Elohim is the immanent light, what enters and is clothed within the worlds. The name Havayah — which is what some mean when they say “the Lord” — is the transcendent light that cannot be clothed within the worlds. Rabbi Chaim Vital, it seems to me, meant, when he said that the Infinite Light filled all the void, that his intention was the Essence. By the way, Hasidic literature was not written in an orderly fashion and depends on context, as I wrote, so in order truly to understand everything, you need to learn all of it, and only then do you see the full picture — provided that you understood it correctly. There are a few people who have complete knowledge in this field. The combination of Hasidism and Kabbalah also helps toward a fuller understanding. By the way, someone who knows the entire Talmud is not comparable to someone who knows only part of the tractates, or just one; when you’ve learned everything, the whole puzzle comes together better. And that is in relatively easy material matters that are easier to grasp and understand. Here we are dealing with deep divine matters. For example, according to Hasidism, cause and effect is not exactly the same as reason and consequence.