The interview process had 7 rounds, mostly repetitive typical product questions. The interviews were reasonable difficulty for the role. I do think though that it is completely inexcusable to ghost candidates after they make it through to final rounds.
A simple, we have made an offer to another candidate email is 2 minutes of effort and is respectful of the time they took up. Know that if you interview here it is likely they will not be transparent or consistent through the process.