I learned Haskell and used it (and heavily functional Scala) professionally for about 6 years.
I feel learning Haskell was worthless. It did not teach me anything about decomposing problems into function units, compositional sequences, pure functions / immutable data structures, lazy evaluation or asynchronous programming that I have found useful in modeling solutions to software problems.
Guarantees from the compiler and use of the type system itself for type designs like phantom types and type class patterns did not help reduce behavioral bugs and the slower development cycle of waiting for compilation (instead of just using occasional unit test runs to check simple safety conditions in lighter weight dynamically typed languages) was a very significant cost.
It was no easier, and often much harder, to enable extensibility into systems designed in Haskell because the constraints of the extensible needs of the system were only ever learned from changing business circumstances after the fact and could not be reflected in anticipated up-front design, which is perhaps the number one need of business software yet is an area where functional languages are uniquely poorly suited even with veteran, highly experienced engineers on the team like we had.
In the end, following simple patterns of composition and function purity while avoiding cookie-cutter design patterns and avoiding use of object / class constructs is all you need. This is easy to achieve in many imperative languages while leaving much greater flexibility to choose mutation, treat safety as a resource to be traded off instead of enforced in all cases, etc.
“Module oriented programming” in Python or C, letting lightweight unit tests replace heavy reliance on type system patterns, just using simple structs / namedtuples / dataclasses that posses zero function logic, and creating imperative APIs around functional-inspired core implementations is strictly better.
Really, strong adherence to statically typed functional languages with lazy evaluation is a religious trap. Learning that it’s not all it’s cracked up to be early in your career is critical for success.