I've had FAANG tell me to read Cracking the Coding Interview, sent me links to leetcode/hackerank, sent me PDFs with notes on what topics would be covered for domain specific interviews, linked me to their blog posts on architecture design, videos by their engineers on how to prepare, given me the literal behavioral questions I got asked, etc, etc. Facebook sent me well over a dozen links to guides for my interview and half of those had further links in them (including to a list of practice questions on hackerank).

edit: It is also very reasonable to study having done it myself and talked to people who have gotten into these companies. At 15 minutes a pop you can do 100+ leetcode questions a week. Spend a few months and you'll have studied almost every reasonable question. Most of them are repetitive patterns but around 5% have tricks you need to memorize. That covers 2-3 out of your 5 interviews. Behavioral you need to memorize around 5 questions that they'll basically give you ahead of time. System design is harder but there's videos for the 10 topics that will cover 90% of the potential questions.