I’m with you that there is no publicly available proof of non-human intelligence. And I agree that the testimony of congresspeople isn’t exactly the best way to ascertain whether something is true.
But I’m not claiming that non-human intelligences are here, I’m merely answering the question posted by the OP: the allegations made by Grusch and other whistleblowers are being investigated by Congress, and that they have shared with Congress testable evidence that has not been made public. That includes program names, names of the people in charge of those programs and the location of some of those retrieved craft.
Everything else is our personal opinion, strongly as we may feel about it. I personally think it is worth investigating these allegations. If the witnesses have lied to Congress under oath, they need to suffer the consequences. But if they haven’t… Well.