Other Resources
I'm not the only person to have done something like this, but I think it's important to highlight people or sites that attempt to also demystify Unreal Engine.
Ben UI / Unreal Garden
It almost goes without saying, but this site was a godsend (and still is!) when I need information that isn't easy to get or when I want to understand something that might not get the same consideration actual engine features do.
Xist / X157
This is an incredible resource that one Xist (as they call themself online) has created in their own exploration of Unreal. It's a lot like this site in that it feels much more like one person trying to leave breadcrumbs for their future self. A lot of the exploration centers around the Lyra Sample Game and goes in depth into the systems that that sample game implements and integrates.