Actors in Elixir (and AFAIK the Actor Model in general) can mutate their internal state in response to receiving a message. It would probably be awkward to use actors in this way just to facilitate mutation though.

Scheme is not a pure functional language. I think you need to check the rest of your notes.

According to Let Over Lambda, Lisp is the least functional programming language ;)

https://letoverlambda.com/textmode.cl/guest/chap5.html

    (define lol
      (let ((a 0))
        (lambda ()
          (set! a (+ a 1))
          a)))

Scheme is a functional programming language in the same way python is. The only difference is that it has tail call optimisation and the stack doesn't have an arbitrary limit on the number of function calls it can hold.