My second job, I agreed on a start date having forgotten that I had a week-long cruise booked for the very next week. It had been arranged a year or so before by a friend and just was not on my mind. So I started week 3 of that job with a -40 hour PTO balance.

Companies have a lot of flexibility in deciding how the accruals work. But, as you said, the important part is that when it accrues, at that point it's a legally-obligated right for you to either receive that time or be paid for it.

One hint is that you only see this in jurisdictions without strong labor laws around PTO. Some places, you have to give at least X weeks accrued a year for all full time employees (might be laddered by tenure) and you have to allow them at least Y continuous days/weeks per year; they may also have to to spend all of their accrued time within a short-ish window (limited rollover).

In this sort of environment, I've never seen a company claim "unlimited".

I don't want accrued benefits. That means that someone owes me 1000s of dollars and I cannot have that debt honored unless I quit my job?

I generally try to work at places that value my contributions but do not try to micromanage me. If I want/need to take time off, I do. If at some point I'm taking off so much time that they no longer feel that I'm contributing enough to the company, then fine they can let me go.