I can't think of any.
Any suggestions?
For a long time there were whispers about a mysterious island where celebrities and politicians would go to diddle kids...
And though there are still disputes about the matter, I think this might count:
The media called the 'lab leak' story a 'conspiracy theory.' Now it's prompted corrections — and serious new reporting (WaPo, 2021) (https://archive.ph/LCadf#selection-335.0-335.119)
White House pressed Meta to censor COVID-19 posts on lab leak theory and vaccine hesitancy, internal emails show (ABC, 2023) (https://abcnews4.com/news/nation-world/white-house-pressed-meta-to-censor-covid-19-posts-on-lab-leak-theory-and-vaccine-hesitancy-internal-emails-show-coronavirus-pandemic-president-joe-biden-facebook-social-media-mark-zuckerburg)
Why the Pandemic Probably Started in a Lab, in 5 Key Points (NYT, 2024) (https://archive.ph/fegkD)
MK-Ultra is a crazy one.
https://en.wikipedia.org/wiki/MKUltra
Operation Paperclip
https://en.wikipedia.org/wiki/Operation_Paperclip
How could I forget
COINTELPRO
https://en.wikipedia.org/wiki/COINTELPRO