The era of so-called “modern” C++ started with C++11, which was a radical reworking of the language. All prior versions of C++ are “legacy” or “classic”. Idiomatic code in “modern” and “classic” dialects almost look like different languages.
C++20 arguably marks a new dialect break but it doesn’t have a colloquial label to distinguish it from “legacy” and “modern” AFAIK. Idiomatic C++20 looks pretty foreign from a C++11 perspective (but is unambiguously an improvement).