Always appreciated these posts as I was interview prepping, so here is me giving back:

Onsite Experience:
Two entierly technical interviews, a behavioral interview (with a short coding question at the end) and a system design interview. Problems were a mix of LC medium and LC medium/hard.

Preparation:
Reviewed all basic DS+A, did ~80 LC problems (on a different account). Reviewed interviwing tips from Cracking the Coding Interview.

Resources:
Awesome for system design:
https://github.com/donnemartin/system-design-primer
Useful for how to approach the interview process:
https://medium.com/@XiaohanZeng/i-interviewed-at-five-top-companies-in-silicon-valley-in-five-days-and-luckily-got-five-job-offers-25178cf74e0f

I have 5 YOE at two other FAANG compannies, and have conducted ~250 interviews over that time.

Tips:

• Only you know how much you have to prepare, I think if I did 100's of LC problems like some poeple do on this site I would go crazy, but really thinking through the smaller # of problems I did really worked for me
• Yes interviewers care about you getting an optimal solution, but they care much more about how you solve the problem which only happens if you talk out loud and explain what you are thinking. I can't emphasize enough how important that is. It may feel unnatural, but really force yourself to do it in the interview and while you are practicing. For every problem I did on LC, I was taling out loud the entire time to myself and explaining what I was doing to get used to doing it in an interview setting.

Offer ended up being a bit below the median on levels.fyi, but it was still very competative and a fair offer considering I am coming from an L4 position so I would expect to be at the lower end of the L5 band.