The ML family is the most reasonable IMO. Languages such as OCAML and ReasonML feel like they’re designed to solve real world problems rather than adhering to type manipulation pedantry.

"Standard" Scala (i.e. without the fancy monadic libraries like cats or zio) and Rust are both mixed paradigm languages with good support for many FP constructs.

In practice you can write imperative code using either of them but the focus on immutable data structures, and (in Rust more than Scala) functional error handling means that many manipulations are easier to do with FP constructs, so they appear quite naturally (Option, Result/Try, iterator maps etc.)

As a bonus IME they are very similar in many respects so experience in one translates well to the other.

Imo, Elm is the friendliest pure functional language. It's a frontend language though.

I'm a backend developer by trade and Elm made me fall in love with frontend development, which I've rather hated before.