Scala Async VS Enumeratum

Who said FP was mandatory? Scala is not Haskell, nor Lisp! If you don't like effect systems and all, don't use them. The choice is yours, actually. Kotlin's coroutines aren't better than what Scala offers. You can even use async/await in Scala. IMO, if you get yourself in a "callback hell" with Scala, then you're not using it properly. For comprehensions are easy to understand, and work with Futures, for instance.

Here is your async/await ;) https://github.com/scala/scala-async

I'm not sure I understand what Cats or cats-effect has to do with what you're trying to do. As far as I can tell, it sounds like what you're asking is simply "what's the best way to implement an enumerated type in Scala?" The best answer to that I'm aware of is Enumeratum.

In Scala 2: enumeratum which is, essentially, option 3 from your post.

And for exactly the same reasons one shouldn't override equals and hashCode in a case class, they shouldn't manually implement an enumeration and instead let a well-tested macro (2.x) or the compiler itself (3.x) handle reliably doing the automated code generation. The more code that is generated by the compiler, the smaller the defects, technical debt, and security vulnerability surface areas.

For Scala, check out the enumeratum library (https://github.com/lloydmeta/enumeratum). In my opinion its the best enum implementation I know of. It has all the features defined in the table, and the syntax is really clean. It even supports unique associated values (eg. unique String/Int keys).