Screenshotting a private message to share it is a betrayal with extra steps.

Taking a picture of somebody’s words and sending it on is a sequence of deliberate acts. You have to open the message, capture it, choose a recipient, and press send, and at every one of those points you could stop. That is what makes it different from letting something slip in conversation. The outcome is the same as gossip and the process proves you meant it.

So treat private messages as unforwardable by default. If something genuinely needs a second opinion, describe the problem in your own words without the screenshot. And notice whether anybody has ever sent you one, because that tells you what happens to yours.