Off the top of my head there's failing to prepare for massive changes to the ads they could run on Apple and Google's platforms and then realising that the money they were making was way less than expected, purchasing a company associated with malware, calling game developers "fucking idiots", growing the company enormously over lockdown and then realising they've pissed all their money away. I don't really know what a CEO actually does so a lot of that could be just company decisions, but JR definitely seems like a loose cannon who can't help being wildly unprofessional.

There was also a bunch of sexual harrassment that was swept under the rug. He's an incredible scumbag and a shitty CEO, which is why the psychopaths that inhabit corporate boards seem to love him

9 years of everyone telling him that forcing the UNITY splash screen on "baby's first game" was a bad idea and was hurting the engine, because people were assuming all games made in the engine were bad, because good games didn't show they also used Unity. Now that he is gone this changes.

Also he is a huge fan of the "metaverse" idea: https://venturebeat.com/games/unity-ceo-john-riccitiello-the-metaverse-will-have-millions-of-destinations/ and I am sure some of Unity's money went there at a time they could not afford it and with nothing to show for it.