The numbers vary but claims like this come from Whistleblower David Grusch:
“Absolutely, based on interviewing over 40 witnesses over 4 years…”
1:07:30 in video of Congressional UAP hearings.
[embedded content]Source: https://www.youtube.com/watch?v=KQ7Dw-739VY&t=5s
And Michael Shellenberger is making similar claims here (paywalled ... Read even more