In my experience, learning a new language makes you much better at the languages
you already know, and each one you learn is an easier challenge than the last -
it helps me understand what is shared across programming vs what is a specific
style (or wart) in a language I already know. So I definitely recommend exploring widely!
In general, I'd encourage you to follow your gut and curiosity - whatever you're
most interested in will end up being less effort/more fun, and likely the most/best growth for you -
so, scratch that itch!
Some different options that you might take a look at:
My favorite by far is Clojure - it's practical and minimal and can be used for
everything (full-stack + scripting), and interactive programming is really nice
(vs the typical write + compile/run-the-world loop). Unfortunately, learning to read/write
lisps is a bit mind-bending and tooling-intensive, so expect to invest time in
your tools before you can really get going with it. (Connecting to a running
repl from your editor is an excellent paradigm for writing code, but it's really
on you to manage and debug the tools that support that workflow, and that's just
difficult at the beginning.)
Elixir is another modern option that'll teach you some new patterns/paradigms, like the
actor model (via OTP) and pattern matching. I'd be writing more elixir these
days if I hadn't found Clojure :)
Haskell is totally different and quite difficult, but generally worth it. It's
especially difficult to pickup without a mentor/team to learn it with. It can be
very minimal and will change the way you think about functions and types (it did
for me, anyway). I don't find it to be very practical (i've become quite
opinionated about strict types), but I know folks who do. I wrote a post
about using 'lenses' in Haskell a few years ago, a glance at some of the code
will show you how different it is from other languages:
https://medium.com/@russmatney/haskell-lens-operator-onboarding-a235481e8fac
Rust is increasingly popular, and for good reason - plenty to find on this,
large community, definitely not bad choice at all from the sound of your path so
far.