Actors absolutely can provide input over writing and direction.

For example in the recent Spider-Man film Tom Holland was in the writers room pitchinh ideas.

On Game of Thrones Liam Cunningham rejected Davos romance with Missandei.

In those cases the actors are already signed on so ultimately the writers and directors have the final say (within reason).

But in this case Depp isn't signed on to a film. So before signing on to a film he has a lot of options for control.