My experience is similar to many others' experiences here. I believe they post jobs and do some interviews to show their presence in the market but do not have much to offer.

I applied for the Toronto opening through someone working at slack. The first round was 30 min HR phone interview comprising of general HR questions. Second round was a 45 min zoom call with the hiring manager. He asked questions about my previous projects and how I collaborated with the other teams. In the third round I had to review a Junior Developer's pull request trying to be as kind and empathetic as possible. The 4th and final round was a 4:30 hour interview with 4 people. The first 45 min session was regarding system design; I was asked to design a chat messenger. The second 45 min session was again with the hiring manager who went a little more in detail into my experience. Next I had a break for 30 min. The third 45 min session was about team work and collaboration. The fourth session was a pair programming session. I was given a link to download code and develop a feature for a private channel. The emphasis here was not on how much I could complete, but on the way I would code in real life. The final 15 mins was a wrap up call with the HR