Status: 5 years of experience
Position: (Senior-) Software Engineer at Microsoft (but offered with 61), SDE2 at Amazon
Location: Microsoft -- Oslo, Norway; Amazon -- Gdansk, Poland

I've been interviewed by Amazon in July. Gave my verbal acceptance. While i was waiting for some documents due to law reasons (unexpected for
me) i got another interview with Microsoft (didn't plan that, just got an email from recruiter).

Amazon

Online assesment:

1. Some general problem involving sorting with custom comparator, filtering etc. Not algo problem.
2. https://leetcode.com/problems/partition-labels/

1 test from 1st problem failed, i didn't realise why, but i passed this OA.

Final round (5h):

1. Cultural fit/Behavioral interview with Manager.
2. very close to https://leetcode.com/problems/roman-to-integer/
3. Close to https://leetcode.com/problems/jump-game/
4. Some simple "Map+one pass"-like problem.
5. System design (Design service for Amazon Alexa). Nothing special, you just have to mention common strategies of scaling, consistency etc.

Got an offer SDE2

Microsoft

Online assesment (Codility):

I got 3 problems:

1. Easy-Medium string problem

2. Some easy problem "Map + one pass" like.

3. Jump Game variation.

   Time O(N)
   Space O(N)

   100% Performance, 100% Accuracy as the result.

Final round (4-4,5h):

1. Cultural fit/Behavioral interview with Manager.
2. Close to https://leetcode.com/problems/valid-palindrome/ and something like that https://leetcode.com/problems/word-frequency/ (Did it well, but i got a bit confused while disscussing test cases with an interviewer.)
3. System Design. Abstract web app, common scaling technics. Went well.
4. OOD.

A week later i got a call told me that "we liked you, but you need follow-up involving Algo/OOD."

Follow up (1h)):

1. Close to https://leetcode.com/problems/combination-sum/ . Solved.
2. OOD. Some general "design API" question, inheritance, interfaces, DI etc. Seems like easy for someone experienced in back-end, but i would say that i was not so good here.

As a result i got an offer, but 61 level.

Summary

In general i feel that i went well. Couldn't give you any new advice, just leetcoding until you feel confident, don't hesitate to solve one problem 2-3 times, it's very useful to my mind.
For System Design part i was watching YouTube, some conferences (Reddit CTO, Slack CTO etc).
I didn't prepare much for behavioral questions, but general STAR method seems to be very concise.

P. S. Please, post your notes in comments and i will update my post. Thanks.