alt Hacker NewsCongrats on finding this. Very impressive for a 15-year-old!
The section "How to Protect Yourself" is lacking.
Step 1. Don't receive this information in the push message. Only send the fact that there is something waiting for you in the app. Chances are there are other vulnerabilities that compromise the end-to-end encryption guarantees provided by the app (and only by the app).
In Signal on iOS: Click on your icon in the top left corner. Click on settings. Click notifications. Click on display below "message contents". Make your choice.
Another situation where convenience clashes with security, unfortunately.
Step 2: If you use Discord, don't allow invites from _anyone_.
Its quite bizarre why social media apps allow anonymous people to interact with you. 99% of the conversation I have is with people that I roughly know.