There is a good list of startups that went bankrupt here: https://www.cbinsights.com/research/startup-failure-post-mor...
Katerra seems like the latest big one - $1.5B in funding that filed for chapter 11 last year.
Homejoy perhaps?
Re:Minsky Moments in Venture Capital
by MichaelZuo on Monday February 21, 2022 @01:12PM
(#30418816)
Wasn’t a unicorn I believe but seems close enough.
I can’t think of any big YC company with a down round + death spiral, but I think maybe one of the Techstars companies?