I once asked hr from a position advertising "unlimited PTO" what was the average of PTO days in the team. She panicked a little bit

Yes, but it also doesn't give any indication of norms around the amount of time off people take.

Expectations may differ from how much time is in a traditional PTO bank but at least in general, it's OK to take accrued time off barring special circumstances.

I live in a state where that's not required, so it doesn't happen anyways. ¯\_(ツ)_/¯

When I put in my two-weeks at my last job, my boss said that if I can get all my work transferred in only a couple days (I did, since I basically had almost no work, hence my search for a new job), then I could just fill the rest of my two-week notice time with my remaining PTO. No reason to spend two weeks pretending to work at my computer.

Yeap, PTO is a liability on the books and unlimited PTO is a way to get rid of it.

Bingo.

The company I'm at effectively has that as part of their unlimited PTO policy, though the timing is company-mandated, being the first week of August and the week between Christmas and New Years, which is a week so many people are likely to take off anyways, it just makes things easier to make everyone take it off.

Going into the week off in August, I wasn't sure how seriously they took it, but sure enough, I didn't get a single e-mail that week other than weekly reports from automated tools. I even checked Slack that Friday, and there wasn't a single message except for the channel where people post pictures of fun stuff they do over the weekend.

It was pretty nice.

Banks tend to have this policy because there are a lot of ways to steel in ways that you can cover your tracks. But most of those ways require regular effort to cover your tracks, so if you are locked out of the office for at least two weeks someone is likely to notice. Note that this is two continuous business weeks. Nothing happens over Christmas so that doesn't count.

In many jurisdictions, there's a statutory minimum amount of annual leave; you can take less but then the difference must be paid in lieu. (Versus if you give 30d, 18d is minimum, and employee takes 20d, then you don't have to do anything. Obviously could have a company policy of paying it if you want.)

So, a more cynical take on mandatory time off, and something that absolutely does happen, is that they'd just rather not have the work than have to pay extra for it.

Also common is not rolling over into the next year, so use it or lose it.

In Norway you're required by law to take four weeks and a day vacation every year. Almost everyone has five weeks vacation time in total. Both you and your employer can demand that three of those are continuous during summer, and most of the country shuts down three weeks in July.

That doesn't necessarily mean it's "unlimited". It could be that you get eight weeks and they just don't say so.