Hello this is Gulshan Negi
There are several functional programming languages but the best one for you will depend on your goals and interests.
I will recommend you choose one from the below list.

Scala: Scala is a hybrid functional and object-oriented programming language that runs on the Java Virtual Machine (JVM). It allows developers to write concise and expressive code while also taking advantage of the vast Java ecosystem.

Haskell: Haskell is a purely functional programming language that emphasizes type safety and lazy evaluation. It has a strong, static type system that can catch many errors at compile time, and its laziness allows for efficient handling of infinite data structures.
Thanks