First 30 mins discussed iOS dispatch queue. I was struggling to understand what he wanted me to write as wheneven I was trying to write something he was telling to assume that it is already written. I think I failed here.
There was no fixed question. I did not expect screening round to have this much for iOS question.

Next 15 mins, one leet code medium tree problem, I solved it immidiately.

I've 10+ years of experience, and I hold master degree.
I solved 250+ leetcode problems, and mugged up facebook's top 150 leetcode.

After the HR Call, I took 3.5 months to prepare. And it seems like all went into vain.