Depends on industry really. You will find Java everywhere, so having knowledge of it will help you just about anywhere. For example payment industry, Android native development, etc. Mostly older codebases will be in Java, but you can find new projects too. Java tends to be used by bigger corporations, so it's almost always a bloated mess.
Python is heavily used in machine learning, which is the next hot thing, so it's a safe bet too. And it's a very beautiful language, even if it's not the fastest.
I would try to get away from JS, because it has the lowest barrier of entry, and the most developers, so it's very competitive and lower paid than the other languages you mentioned. But it's the gold standard in front-end, so if you like that you can learn React or Vue. You can also incorporate Typescript if you want to.
I wouldn't try to get into C++ either. Rust and Go are gaining traction in the same areas that would have used C++ traditionally, so I think either of those are a good fit if you want to do exclusively backend work.
What kind of industry or area are you interested in?
LLM will need a source of truth, like knowledge graphs. This is a very good summary of the topic, by one of the wiki data guys: https://youtu.be/WqYBx2gB6vA