Help me find information about scandals, security problems, and failure to respect users involving these proprietary social media apps

Hey! Following the #GlobalSwitchDay initiative, can you share any scandal, security problems or situations in which the proprietary apps have failed to care for their users? I would like to gather information for each app so people I know can be more informed about what they're using. Mention things that you might even take for granted, some people are completely unaware.

The apps are: Whatsapp, Reddit, X/Twitter, Instagram, Facebook Messenger, Facebook, YouTube, TikTok.