I had something similar years ago. I applied for a job at a company, size around 150 people. Did two rounds of interviews which were great. They wanted me to offer the role. However, as a third round, I was going to do a meet and greet with the CEO and he was going to yay or nay me. At point I dropped out. If a CEO can't trust his delegate managers to hire the people they see fit for a role, then thanks but no thanks. That's not a company culture I want to spend most of my waking hours in.

I don't know your particular situation, so it might be totally different, but I think this is commonly just a formality and a friendly chat.

It's a chance for you to meet the actual CEO (or VP or whatever in a larger company), and also for them to get to meet you in advance, instead of effectively getting "blindsided" by a new person (to exaggerate a bit).

Usually, by the time you've gotten to that point, the decision to hire you has well and truly been made. I don't know what then would need to happen for the actually rather secondary function of giving the CEO the opportunity to veto to become relevant. I'd be curious hearing about anyone who's ever experienced it (on whatever side). I guess it can be a safeguard against vastly unaligned values, but I suspect it's very rare.

But primarily, and effectively, it's usually just a meet-and-greet. And it's hard for me to blame a CEO (or VP etc.) for at least getting to anyone who's going to enter a mutual contract to effectively become part of their company.

If you got to the that point it's just a formality, and unless you somehow blow it the job is (probably) already yours, if you decide you still want it. You seem to have jumped to unwarranted assumptions about the company culture; quite possibly the CEO does want to make sure the culture is good and remains good. It's not necessarily a binary test of whether the CEO can't trust delegating to their managers; it's also your constructive opportunity to use that conversation to get more insight into where the company, strategy, product/service, customers etc. are going. A good question to ask the CEO is about the broader impact of your role: that should get you some useful insight, also you compare the delta between what the CEO says vs what the senior managers said vs what the recruiter said; they don't need to be identical but they should broadly agree, and it shouldn't reveal any fundamental disagreements or ambiguities (e.g. "your role is incremental support of product X" vs "totally rewrite it in language Y in the next 9 months"). Listening to their response should also give you subtle behavioral cues about who in the company does/doesn't have influence, credibility and where the pain points are: you can't generally get that from the previous interviews, and it can be a faux pas to explicitly ask.

The only (minor) negative I'd take from this is that it still behaves like a small startup scaling quickly, and they haven't yet figured out how to to scale interviewing and hiring for when they get larger... but that's overall a good complaint, it shows they're still growing. It's much better that your signoff interview is with the CXO (or VP) than the Director of HR, or an AI bot.

Don't overthink.