He covers some questions in the video, but i think if there's some practice material, it would help in assessing and improving concepts that learnt through these resources

I don't think doing practice questions would help you much unless you're interviewing at a place which asks textbook JS interviews and make you do whiteboard stuff, if your fundamentals are rock solid, you can pretty much crack the interview with no formal preparation. And fundamentals get strong only by working on real stuff and reading architectural documents like one linked above.

I recently found a question like, the point of this question was the

fact that instanceof only works for Objects

, these facts either one remembers through practice or usually when using in day to day work. Should i focus on such questions or good companies usually avoid such things ?

let a = "abc";
let b = String("abc");
console.log(a instanceof String)
console.log(b instanceof String)