> freestanding requires almost all std library.

have you actually read the page you linked to? None of the standard containers is there, nor <iostream> or <algorithm>. <string> is there but marked as partial.

If anything, I would expect more headers like <algorithm>, <span>, <array> etc to be there as they mostly do not require any heap allocation nor exceptions for most of their functionality. And in fact they are available with GCC.

The only bit I'm surprised is that coroutine is there, as they normally allocate, but I guess it has full support for custom allocators, so it can be made to work on freestanding.