The questions are very predictable. Write some python scripts for the OA, it is as described online. If you really care about getting in, find someone that does the interviews a week ahead of you and you will crush them. If you can't find someone buy recorded interviews, some sell them. While I didn't get an offer last year, I followed the steps above to get it this year. Optiver is completely unable to assess candidates based on their skill level. They only check if you answer their set of questions.
Don't get me wrong the interview is hard if you don't know what is coming but I know from 4+ people that each got the same question. I did not take the offer as I've never felt so uninspired by a company. Go to JS or Citadel or any other company.