I'll also add that Haskell, Clojure, and other functional languages will help you think in an entirely new way to program. Python or Ruby are also less mind-expanding, but was a nice change of pace for me at least from my C# day job.
Learning window functions and more advanced bits of SQL that an ORM doesn't give you for free can also be a fun time, along with getting deeper into what indexes can really do.
Elixir shines at concurrency so it will feel more like nodejs and similarly runs on a VM like Node or Java.
Elixir, like Rust, will help with learning functional programming paradigms more than Go.
It's true that as a beginner you can simply do web development with Phoenix and that feels similar to Rails (Or Django / Laravel / Spring / whatever web framework ). But OTP requires a different way of approaching problems.
Elixir is the new Erlang. Ruby is dead (I used to <3 ruby). Go is the new python, zig is the new c, and rust is the new c++.
It's not that it's functional (that's completely secondary in Erlang) but its fault tolerance primitives (processes, pids, mailboxes, monitors and links) and the OTP abstractions (GenServers, Supervisors, etc).
You learn to think in terms of distributed systems and think about fault tolerance in a way you cannot in other languages as they don't provide the primitives. It's quite a big leap and it takes time to sink in.