C++20 coroutines demonstrated one side of committee-led modern C++ that left an impression of it is ultimately designed-by and -for library writers; instead of being suggested third-party library or "wait for C++23" for better experience, I'd love to see these related machinery released the same time in the standard library.

Alternatively, you can pass the things you would have captured instead as arguments to the lambda (by value!) and they are valid for the duration of the coroutine. So you can do a lambda returning a coroutine lambda like

  task<Foo> t = [foo]() {
    return [](auto f) -> task<Foo> {
      co_await something();
      co_return f;
    }(foo);
  }();