Comment by munchler
It can do GUIs well, although it takes some finesse to manage user state in an immutable-first language. Check out Fable for building web apps: https://fable.io/
I don't have much experience with Scala, but I think the two languages are pretty comparable in their respective ecosystems. The biggest difference I'm aware of is that Scala has typeclasses and F# does not.
F# is not really that strong on immutability, though. Sure, variables and struct fields are immutable by default, but making them mutable is one keyword away. Similarly with classes - declaring readonly properties is more concise, but when you need a read/write one, it's readily available.