What other programming language should I learn in order to advance in my career and get better at programming?

So I've been a fullstack dev with C# and JavaScript professionally for 3 years now, and 1-2 years experimenting with them before, in college. I am far from an expert at them, but I do know my way around them. I would like to learn a new programming language, along with popular libraries/frameworks that come with it. The reason for this is that I want to have a bit of fun and novelty in my personal coding time , but also get better at programming and maybe advance my career. Also, it would be nice for the language to be fairly new.

I think there are 4 types of languages from which I want to choose:

  1. Another GC language: the main one I'm thinking of here is Golang, because of it's uniqueness. There's no point to go for Java/Kotlin here, for obvious reasons, neither Dart or Swift because I have no interest to go into mobile stuff.
  2. Another interpreted language: main ones are Python or PHP. Again, no PHP, for obvious reasons, Python remains, but Python seems like a boring choice. Lua might be a choice though.
  3. Non GC languages: Rust and Zig come to mind here. Rust just seems a bit too much, I don't want to put in a stupid amount of hours into learning a new programming language. So Zig remains.
  4. Functional languages: there are many options here, like Clojure, Elixir or Gleam. Gleam seems the most fun out of these though, just because of it's fun website:)

So, remaining in the web/cloud domain, what could be a good choice here? What, as a seasoned developer in the future, could I use alongside C# and JavaScript in order to make myself more valuable, but also have a bit of fun right now learning it.

Golang is a strong choice, but I already have C# which is a language that has very similar use cases as Golang for web/cloud. Lua, idk how it will help me. Zig might be fun, but I hardly see it evolve into something that could have web/cloud use cases. Rust does, but as I said, I wish not to touch Rust. And the functional languages do have web/cloud use cases.

So the strongest options here are Golang or one of the functional languages. What do you guys think?