>> no, you can also call ntdll (or even syscalls although those aren't stable), there's plenty of documentation on the internet

> I mean officially. Yes, you can find some on the internet, but nothing on the official MSDN.

It seems that changed. https://learn.microsoft.com/en-us/windows/win32/devnotes/ntq... says

  [This function may be changed or removed from Windows without further notice.]

but it on the official MSDN site, and it does document a call in Ntdll.dll.

It’s easy to find many more examples such as https://learn.microsoft.com/en-us/windows/win32/api/winternl..., so I don’t think that’s an accident.