What legal documents do I need to provide before joining FAANGMULA on an existing side hustle?

Today during office hours Rahul talked about this a tiny bit (sans the legal), but I'm curious as I've had many friends who worked at Google previously that discouraged me from applying to Google (like 10 years ago) if I still wanted to do a startup (this was long before Area 120 was a practiced thing). Recently, a friend (VC whose girlfriend works at Google) said many people still build venture/angel funds on the side while still working full time for Google. But of course, don't create your startup company using company property (a la Silicon Valley HBO lessons).

Questions

(1) What companies are flex about having things on the side - a side hustle (but you can't advertise it), examples being two different companies on both ends of the spectrum: Google, Apple etc.)? I've heard some FAANGMULA companies are more stringent than others (Apple being very much against this and super private and only sorta kind supporting open source, vs. others which are all for it and have accelerator/internal incubator programs at the company (Area 120), or even sponsoring ex-employees (a cohort of my class at Verizon Ventures one year was all MIT alumni, ex-Googlers that were sponsored by Google, paid their incorporation fees, I was one of the two weird VR founder people).

(2) I've also heard that from friends if you work at Google, you are not allowed to get paid for speaking gigs on your technical expertise or whatever your functional role is at that company (this differs from from Meta I've heard from other friends). Is this true?

(3) If you go into a FAANGMULA company, what info (legally) what information do you need to provide the the employer? What docs from the state/federal/govt or whatever) that says you have a a DBA, LLC, S/C-Corp etc. What do you need to disclose more specifically and what documentation and legal paperwork do you have to provide?

For example, I currently take consultations and speaking gig money and have revenue (royalties from my book I published years ago) and plan on having an existing app that generates money in the app store that is runs auto-pilot prior to coming into the company. Also note, that I'm aware that this product should not compete with the company's main product lines.**

(4) If you are going to start all this AFTER being hired into FAANGMULA, how do you inform your company employer formally (HR, direct report boss), and that your side hustle does and will not interfere with your primary role at the FAANGMULA company hour wise and that you will still meet all of your core duties/goals/tasks/deadlines for the company and this is sort of 'hack on the weekends thing?'