Could it be that cryptography is CPython only? - Yes, that’s what’s happening here. If you look through the dependencies that pip is trying to install, you’ll see that it’s getting stuck on cffi. The cffi package is a “C Foreign Function Interface for Python”.
As mentioned here, I’d definitely explore system.net.httpClient. It can do most of what requests does, and is normally really good at it. It might be a little less ‘pythonic’, but it’s very capable, and even gives you access to the underlying HttpClient / HttpRequest / HttpResponse objects if you need them.