Whole process went for 4 weeks, online. It's split into 4 interviews: Screener with HR, RRK (Role Related Knowledge), Googleyness + Leadership and GCA (General Cognitive Ability/Problem solving). These last two I had on the same day with a few hours difference.
I would give you advice based on my steps, but I failed, so... Nonetheless, I would suggest you to look up Youtube videos on the subject and to prepare yourself with mock-up questions + follow-ups. The GCA especially is very difficult, and demands you to be at your mental best in terms of problem solving and understanding. Do not take it lightly. Don't prepare specific questions, but instead prepare your thought process and always, always think like you're already on the role. All questions, even if unlikely, are directed to your role.
My experience with all interviewers was positive, and they were pleasant to have back-and-forths with. Both RRK and Googleyness went great, but GCA was the reason for my rejection.
One thing to keep in mind is to not bother asking your interviewer how the interview was/how you did, because it means nothing. At the end of my GCA I asked the interviewer what were their thoughts were about the interview, and was told I did "very well" and that they got "good insights into how I think and problem solve". Yet here I am without an offer, so make of that what you will.
Speaking personally, I also feel it was a bit unjust, despite knowing my performance during the GCA wasn't exactly stellar, even if I did my best to prepare, I know that at least out of 3 interviews I did great on 2. But it's a ruthless process.
Also, no matter the outcome, there is absolutely no feedback related to your performance in the interviews, even if you ask your recruiters for it. They just tell you where you failed.
All in all, to sum up, prepare yourself mentally as much as you can and don't be afraid to take time to think out a structured answer.
Good luck.
You've got this.
You can do this.
Succeed where I failed, and make your dreams come true.