They got emails from FOIA, this is not a "prove" thing, it is public documents.
Many scientists were concerned with artificial origin but forced to go with political message and when publishing the proximal origins paper the goal was "disprove lab leak" not find the truth.
Related FB & IG suppression of lab leak mentions by CDC moderation happened all over the world including the UK. I won't duplicate the links but those are reputable sources. Your opinion was shaped by US left.