No one else bit, so I’ll bite.
First of all, you say that you “have knowledge about” a few programming languages. I don’t know what that means.
When learning computer programming, there are two issues, learning a language, and learning programming. The second part will be almost entirely common to all languages. If someone wants to learn “how to write a mystery novel in French” - there are two questions: Do you know how to write a mystery novel? Do you speak French? After learning those, if they want to write a mystery novel in Swahili, they just have to learn Swahili, they don’t have to learn the structure, pacing, cliches, etc. of a mystery novel again. Computer languages are like this - there is a difference between the language and the programming. When people say “advanced JS”, what they often mean is “advanced programming using JS”.
Really, I think the best way to learn JS is to learn the basics and then start using JS. When you code, you will encounter problems and find solutions. You will get good at search MDN and Stack Overflow. In parallel with that, you might check out some books, watch some videos to get ideas, fill in holes, etc.
The MERN stack is a good goal. It’s what FCC teaches, it’s what I do (learned from FCC). But again, if you follow that curriculum, you will learn the basics of JS as you go and apply it. If you don’t want to follow that path, then just do as I said before - learn the basics, start to use it, do a little side research in parallel.
And most of the MERN stack won’t require “advanced JS”. You will need a solid intermediate level JS, imho.
But again, I’m still not clear what “advanced JS” would be. JS doesn’t get that complicated and arcane. Programming - absolutely! But the JS language? It’s more that there just may be some things that you don’t use as much.