I haven't seen any proof yet.
If this is about David Grusch the whistleblower, the stories are interesting, but I'm not entirely convinced. He's provided no evidence, and his statements have been "cleared for open publication" by the DoD. If he's been cleared to say all this, then it could easily be a false front. A story to divert attention from programs that the US wants to keep secret from foreign powers.
The military has done this before (look up Richard Doty). It's even possible Grusch himself believes in all this, maybe even was groomed to believe, but either way his coming forward isn't actually whistleblowing. If I'm not mistaken, from what I've read, the information he's revealing was told to him, not experienced by him firsthand.