In this degenerate example, the completely straightforward way is tied for fastest as well. It's clear this has nothing to do with ranges.

    Response response;
    response.data.reserve(widget.data.size());
    std::ranges::transform(widget.data, std::back_inserter(response.data),
        [](const auto& element) {
          return ToData{.title = element.title, .amount = element.amount*42};});
    return response;

> the completely straightforward way is tied for fastest as well.

Is it, though? back_inserter should replicate push_back(), which incurs a move at the very minimum. The approach with emplace_back() does not.

https://quick-bench.com/q/1zwemArsS0gtKwveR9FZsuRwT34

This also isn't the way C++20 wants us to work with ranges and views, either -- this is basically just std::transform as you'd write it 20 years ago, except with a container as the argument instead of your begin / end iterators (so, basically absl::c_transform).