I'm from Brazil and got curious about the "unlimited vacation", how it works?The U.S. is the only advanced economy without a vacation floor. (To join the EU, 20 days is the lower limit.) Three weeks is typical for an average job (but some companies are sleazy and pool sick time and vacation under "PTO") and two for a crap job.
It's surprising how reliably you can predict the quality of a company and job based on vacation allotment. Four weeks: solid, professional, you'll be treated as an adult. Three: average, mediocre. Two: dysfunctional, run the fuck away. Subtract one week if they use that pooled bullshit ("PTO") where sick leave is deducted from vacation. It's a horrible policy, because it means people come into work sick and everyone gets sick more often, but not only is it (shockingly) legal in the US to deduct sick days from vacation, it's not all that rare.
Generally, the assumption is that you should get one week off per decade (e.g. 2-3 weeks in your 20s, 3-4 in your 30s, 4-5 in your 40s) and that, if you have less than that, you're probably too old for the job you're in (you should be further along). That's not a legal requirement. It's just the cultural expectation. If you're 50 and you're still on two weeks, you haven't succeeded at life.
(It's different for consultants, who get no "paid" vacation but charge a higher daily rate. They can generally take off when they want, and can make more than most salaried people working 100 days/year. If you can pull it off, that seems to be the way to go after 40.)
Some startups have undefined vacation policies. This can be really good (if there's a positive culture) or really terrible (if it devolves into a race-to-the-bottom dynamic). It depends. (The one company, with more than 50 people, that I worked at with "unlimited" vacation was terrible. That's not casual, of course, and it's just one data point.) Better is to set a guideline (4 weeks minimum) but allow exceptions.
In software, the more talented people (until they can become independent) solve this by working "from home" and doing a bit of working travel. Free of office distractions and interruptions, you can actually accomplish more in a 3-hour "day" than most people get done in their 8-10. The downside of WFH is that you're still expected to be available during the full 8 hours, and if people get the sense that you're getting your work done in three, then they ask why you didn't ask for more work.