OCaml classes and objects are (ironically) rarely used and generally discouraged. There are some cases where they’re practically required, such as GUI and FFI (js_of_ocaml). But otherwise, most code does encapsulation and abstraction using modules and functor modules (which are more like Haskell and Rust typeclasses than traditional OOP classes).

I don’t know much about F#, but last time I used it most of its standard library was in C# and .NET, so F# code would interact with objects and classes a lot. AFAIK F# also doesn’t have functor modules, so even without the dependence on C# code, you still can’t avoid classes and objects like you can with OCaml (e.g. you can’t write a generic collection module like `List` or `Set` without functors, it would have to be a collection of a specific type or a class).