NTDLL should be stable since it's well documented, and many functions redirect to Ntoskrnl.exe, and things like kernel level drivers call those functions. Those functions won't change without the drivers breaking.

Then there's "Win32u.dll". These correspond to API calls from User32.dll, Gdi32.dll, etc. This DLL didn't even exist during the Windows 2000-XP era. This stuff is not well documented, and I don't know if this is stable.