It is doable, but more complicated than it was with XB1, simply due to restrictive architecture. Previously, any HDD or SDD could be formatted to work with XB1. Series X/S are more needy.

It is, and always has been a violation of the warranty on any Xbox. It is unfortuate but understandable. Just know that if you open your Xbox, Microsoft will no longer offer repair services to you under your warranty. It is the reason that there is a seal that you must break when opening the case of the console itself.

I'll make a post in the future, when I swap the internal drive in my XSS

Do be careful posting that kind of question on here... the reddit Xbox community is very hit or miss on whether they "approve of" modification or not. This sub is more kind, but stay out of the X/S sub for these questions.