Most interviews unfortunately have little to do with the actual work and require significant practice to do well.

> One question I was asked was "How do you make sure that a celebrity's tweet reaches all of her followers in less than 3 seconds?". I had no idea, I have never handled that kinda scale.

If you're technically competent overall, you should be able to learn enough to make your way through this from a few hours of reading and watching youtube videos. That's what I did when I was in the same situation, and I passed the architecture interviews at multiple FANGs.

Same for the coding questions. You need to spend time reading interview books and doing leetcode.