In my experience, FB had the best interview process I’d ever encountered. Lots of opportunities for preparation and feedback with the recruiters, incredibly responsive and quick to continue to next steps.
There are 3 stages with a few different parts, some that repeat. Expect to do a phone screen, portfolio presentation, app critique, whiteboarding challenge and background/behavioral interview. Highly recommend meeting with your recruiter for a dry run as they do provide good insight into what to expect and what to focus on.
For app critique I didn’t actually get to pick my app. Not sure if it was because they were trying to check my level, but it was a fun experience regardless.
My entire process lasted about 2-3 months, with some being me wanting to have more prep time.