Perhaps it doesn't need a name since there is only one in German. But a similar construction exists in English, except English doesn't have a special word, just "the" placed in front of comparatives. (For example: "The more we get together, the happier we'll be.") I think the name of this and similar constructions in German, English, and probably other languages is either "parallel comparative" or "double comparative". Unfortunately, while "double comparative" seems to be the more commonly used term, it's also used to describe expressions like "more better", which are used in some non-standard forms of English. (See this Yale site.) To me the real test is whether you can look up the term in Wikipedia, but I didn't find either of these terms or any other term under which the construction is described. So while I agree that while the construction should have grammatical name, I wasn't able to find one that really satisfactory. Wiktionary also suggests "comparative correlative" and "conditional comparative", but again, neither of these is listed in Wikipedia. Since this isn't a feature specific to German, perhaps the Linguistics Stack Exchange would be a better place to ask.
But if you want to categorize the words "je ... desto", together they form what would be called a two-part conjunction. Unlike other conjunctions, it doesn't require actual clauses, but can be used with bare comparatives, so using it often results in a sentence with no verb. Assuming verbs are used, the one in the "je" clause goes at the end, so it's technically a subordinating conjunction. At least it's described as one in this Herr Antrim video.
x ∝ ysindxundylinear. Vergleichex ∝ y^2, x proportional zu y^2 oder "x geht wie y^2". – infinitezero Oct 02 '22 at 08:50