There is no way to do E2EE on a traditional social media platform with user-generated content and comply with existing US law.
You can’t moderate an E2EE platform.
Aside from the fact that you can get Metadata and that some communication frequently happens outside of E2EE - what US law do you believe mandates moderation? I'm curious.
What law do you believe supports your perspective?
All of Meta’s major properties (Messenger, Instagram, WhatsApp) support E2EE messaging.