I worked for a YC founder (won't name it ofc) on a project that went through its pipeline with a big success around 10 years ago, although for me it was evident that the idea was unworkable and i wondered how could they raise funding. As it turned out, one or both of cofounders had criminal convictions before, one of them actually came up with the idea of that product while in prison, they completely faked all their user and traction numbers and siphoned money out of investors, and almost everything that was ever actually done, was done by a single developer i have supplied them. Then they were uncovered and went into hiding again (probably always used fake names so idk if it even matters - maybe they are still around us).
Ironically, the idea that was unworkable back then, appears to be still unworkable, and is still actively tried by one team i talk with! And they recently raised money from Google.