> Depends on when it was. (...) Nowadays, most tickets go to hackerspaces and volunteers but the open sale sells out in seconds.

2016 and 2019. That's how it was back then as well and that's what I meant by "you have to be fast" - fortunately the ordering system is reasonable and you don't have to type your data in within seconds, all you need is to be there in time. Back then there were three open sale rounds (but I see there were just two last year), I got my tickets in the second round for 33C3 and in the first one for 36C3.