Next session, we may want to kidnap someone who's asleep without waking up others in the same room. So, spells with Verbal components (like Sleep) seem impractical. Our favoured strategy for now is carefully waking them up (with the Mage Hand from Telekinetic), cast Hypnotic Pattern once they open their eyes, use Portent to make them fail the save, then carry them away with Telekinesis that was cast upfront (Stunning Strike+Grapple (the Monk has Grappler) could also be an option, but the DM could rule that Stunning Strike is noisy, and it only lasts for one round instead of a minute). Now, Incapacitated states it prevents speech, but not vocalizations in general. Could the victim in this case scream to wake up the other person in the room?

(the one data point I would have is that, in 2014 rules, Stunned stated the afflicted could "speak only falteringly", which I would interpret as also preventing loud vocalizations in general, in 2024 rules that part was moved into Incapacitated rather than being specific to Stunned, but now I am not sure how much it prevents use of vocal folds overall)

Up to DM. An Incapacitated creature is speechless and can’t speak so i would also include scream.

Speechless. You can’t speak.

I mean, I guess the question is, how specific is "speak" intended to be (like, is it the meaningful use of verbally representable language through vocalizations? Or just vocalizations in general?). You could argue it's like a temporary Broca's aphasia, in which case they could still scream. Of course up to DM in the end, but our DM tends to be swayed by arguments made in forums, so.

The DMG advises a good faith approach to the rules and applying them. What do people generally mean by speaking? Not the dictionary definition or anything like that, as in if you asked someone outside of the context of D&D "Is a scream speaking?" what do you think the genuine response would be? Then apply that to the rules.

In my opinion no, screaming is not speaking and I don't think I know anyone who would say it is. I think it's reasonable an incapacitated creature could scream.

I'm going to suffix this with pre-empting the dictionary definitionist crowd. Yes, some definitions for speak include "to convey...an emotion" and some might argue that a scream is conveying an emotion. I don't think this would be a good faith argument and not a sound base to appeal to for running a fun game of D&D.

I absolutely agree that the intuitive answer to "does a scream qualify as speaking?" is probably the 'correct' one, I'm just not sure what mine would be. Although there's also the question of whether screaming makes sense when you're in a trance, which is apparently what the effect of Hypnotic Pattern is meant to be (on the other hand, if you were just hit by a Stunning Strike, which also applies Incapacitated, I imagine you probably might scream in pain, so, I feel unsure).

I guess my question to the player would be "Why is your character screaming while incapacitated by Hypnotic Pattern?" IMO that would betray the real motivation which sounds like an attempt to skirt the intent of the rules. There could be a multitude of answers, such as

1. My character would find a magical enthralling pattern terrifying and thus would scream
2. I want to be able to do something
3. I want to communicate that there is something dangerous here
4. My character randomly likes to scream

As a DM my responses would be

1. The pattern renders you so fixated that even your fear is suspended and you can't scream
2. Let's not get into the habit of doing random things for the sake of it as that devalues the game
3. Nope, no communicating. Not getting around the "can't speak" rule
4. Let's not get into the habit of doing random things for the sake of it as that devalues the game

Well, it would be 3 in this case ("someone is telekinesis-ing me away, I can't do anything, please wake up and help!").