It's sad but yeah it's true that you have to prepare for interviews. The reality is that the breadth of topics that you have to have good knowledge on is larger than the scope of work you've probably been working on in your current job.
I had work at a FANG before, but after a few years doing a startup, I had to go over and learn topics that I had no understanding on to get good offers again. I summarized what I felt were useful tactics for prepping system design interviews here (https://www.reddit.com/r/cscareerquestions/comments/kd13sx/s...) and a summary on a list of core topics I put together here (http://gum.co/sysdesign).
I had work at a FANG before, but after a few years doing a startup, I had to go over and learn topics that I had no understanding on to get good offers again. I summarized what I felt were useful tactics for prepping system design interviews here (https://www.reddit.com/r/cscareerquestions/comments/kd13sx/s...) and a summary on a list of core topics I put together here (http://gum.co/sysdesign).