Screenshotting a private chat to share is breaking into a house that someone left unlocked for you.

Someone typing to you alone is writing in a room they believe holds one other person. That belief is the only reason they phrased it that way. Moving the image changes the room after the fact, and there is no version where they get to edit what they said for the new audience. The trust was the door, left unlocked for you specifically.

If something in a chat genuinely needs another person to see it, ask first. If it involves somebody’s safety, an adult is the right call. Everything else stays where it was sent.