it's usually just a meet-and-greet.
Yes, it usually is. But in this case the problem was that the CEO could unilaterally override the decision made by everyone else, so it wasn't just a meet-and-greet.
That is exactly the assumption I was operating under, I even called it a "veto". Does not change anything I wrote.
(And of course the CEO can override any hiring decision anyway. The question is if they will.)
Yea, it's not a meet-and-greet, as in there can be no impact to the outcome of the interview. You're definitely still interviewing. But, in every case where I got to the point of "You're going to chat with the [Founder|CEO|BigTech VP]," at that point the job was mine to lose. They're not going to waste a VIP's time if they're not serious about making you an offer. You effectively have the offer. Your job when talking to the VIP person at the end is to "sound like a likable, competent person, who VIP would be cool with saying 'yea I hired this person'." That's pretty much all you need to do.
Generally the chat with the VIP means: "You have the job, but I (VIP) want to just double check that my underling hiring managers are not totally useless."