Creating functions is one of the most common, basic things you do in JS and if you are creating functions then you are dealing with scope, so I don’t think it is accurate to say that beginners don’t need to worry about it.
Yes, it is valid JS, no, it is not a best practice and hasn’t been for quite some time now.
I’m not criticizing FCC here, I know this site has been around longer than the ES6 updates were implemented in all the browsers and so all of the beginning stuff still uses
var. But in a perfect world it probably shouldn’t any more (and from the above comments it sounds like they are in the process of removing