Linkedin, https://en.wikipedia.org/wiki/2012_LinkedIn_hack

Yahoo, https://en.wikipedia.org/wiki/Yahoo!_data_breaches

Or if we don't limit it to just data breaches but include compromises that would have allowed a full account takeover of any account using this identity provider in a third party app:

Apple, https://bhavukjain.com/blog/2020/05/30/zeroday-signin-with-a...