A recruiter reached out to me a week back for backend position at AWS. I had my online assessment today.
90 mins - 1 difficult and 1 moderate question.
15 mins - explain your solution and give the time complexity of your solution
15 mins - questions on leadership principles of amazon ( this was generally how strongly you agree or disagree with a statement)
For the last section do read what their leadership principles are and you should be fine.

My both questions were related to trees and graph. Hence I would advise to do them thoroughly.
I was able to do the first question easily but it is the second one that took most of my time and I had issues with.

1. The first question was number of islands - https://leetcode.com/problems/number-of-islands/
2. The second question asked to return critical servers that need to have a backup, it dealt with Tarjan's Algorithm- https://leetcode.com/problems/critical-connections-in-a-network/

Hope this helps !