[anon-3988]

Hyrum law would dictate that your C++20 now becomes C++11 or whatever is the oldest in the whole chain of dependency.

[Maken]

That's kind of the point of C++'s retro-compatibility: C++20 contains new additions to the C++11 standard. Unless you rely in mistakes in the standard like auto_ptr or faulty atomics, which should be fixed regardless of the C++ standard, your C++11 dependencies are perfectly valid C++20 and do not block the new shiny toys.