Characters that come to mind are Diego from Umbrella Academy and that one guy from IT, but both are again characters who only stutter when nervous and the stutter is also not exactly right. Last character I can think of is Crazy Jane from Doom Patrol. She is basically several characters in one and one of her alter egos stutters and not just when nervous. And imo it's also acted pretty well, the blocks seem very believable unlike from the other two mentioned characters. I think it's good that we finally moved past the "This character stutters for comedic effect/to make them seem dumb" but people still don't do enough research of stuttering. And they also don't have the balls to make a character who constantly stutters.