The question is not about what is possible, it is about what is common. Also, I am not saying the SAD is good or even better than vegan. Anyone trying to eat well is likely to make some of the same good choices, such as reducing refined sugars, dropping a portion of their ultra processed foods, and monitoring and meeting their protein needs. Being unable to hit your protein needs on a vegan diet is something an incautious person may experience, but supplementing protein or increasing protein components in your meals is manageable.
That all said, it takes extra work. Most people don’t have the spare effort to cook at home for every meal, people are time and money poor and stressed beyond all reasonable limits, so we need to try to make some sort of plan that can actually be followed, not just some ideal. Is vegan possible? With effort and education it seems that some people can manage it, so at least some portion of people could do that. On the flip side if someone eats fish and chicken as their meat rather than beef have they not made progress from a bunch of ways? Definitely fewer carbon emissions. I don’t claim to know the answer for what we should do but saying “do this perfect thing” seems counterproductive.
I don’t know about videos but having a look at the OSI model is a good way to start. It covers the abstract framework for packetizing data including things like the distinction between hardware and software, envelope, encryption, application layer stuff, the whole shebang. The cool thing is by going hardware, network, application you can see where responsibility are and it helps you understand where things can go wrong.
If you are interested there are plenty of CCNA style courses available on the internet, licit and otherwise, and they go into more depth, and the same applies to RHCE/RHCSA material. The training for certifications like that covers what you want to know but also puts it in context, and again licit and otherwise sources are available.