To my understanding the C++20 coroutines are very similar to what we have in D using Fibers.

How could I interop with a library exposing this kind of functionality in D? I haven't really used C++ coroutines but I would like to have some sort of compatibility with the standard C++ types for libraries.

See
https://lewissbaker.github.io/2017/09/25/coroutine-theory
https://lewissbaker.github.io/2017/11/17/understanding-operator-co-await
https://en.cppreference.com/w/cpp/language/coroutines