The Elephant in the Room
The "elephant in the room" is a big problem or issue that everyone knows about but doesn’t want to talk about.

Examples:
1- At lunch, the elephant in the room was that one friend had just lost their job, and everyone knew it, but they didn’t want to make them feel uncomfortable by bringing it up.
2- At community meetings, the elephant in the room might be systemic racism, which can be an uncomfortable topic for some but is crucial to address for real change to occur.