Edit: tl;dr View the linked thread, revert to an earlier version of the C/C++ extension.
Have you tried building some code yet? As it’s possible the full toolchain is not installed yet, hence the ‘error’ from IntelliSense. It’s also possible you’re facing a similar problem that others have recently raised, with IntelliSense not behaving properly in the last couple of revisions… Thanks Microsoft! The last two or three posts show how to stop extension auto-updates, and then revert to an older version of intellisense… 0.26.0 seems to be working better for some - doesn’t seem to bother my system, but who knows, mine will probably break tomorrow now that I said that!
Anyway, whilst it’s annoyance, if the code compiles, it is just that for now, an annoyance.