check if you enabled include juce namespace in the projucer. typically it’s disabled to prevent ambigousity problems
This looks like a long-standing problem where IntelliSense doesn’t recognize juce modules because the headers are auto-generated (more info here). Chances are that your code will compile fine, even when IntelliSense is going crazy with error messages. If your code won’t compile, then look through the error messages for ones that aren’t in Juce files. This can be a real pain as there might be hundreds of false-flag Juce error messages. But when you find the real error, they will magically go away.
Devs please take note–this problem isn’t going to go away by itself and there are more and more new users stuck on it.
Could this also be caused by the JUCE paths being wrong in Projucer?