As much as I hate WhatsApp - and I really, vehemently do - I'm pretty sure it is E2EE. Facebook/Meta doesn't directly have access to the contents of your messages or shared media. If you have any evidence to suggest otherwise I'd love to see it.
Problem is, I don't know if it's still set up like this but it used to be that received photos were saved to your device gallery, and perhaps even backed up to the cloud with your camera photos, depending on your setup and device. So the photos might leak through there, but they don't leak through Meta.