Complex Enterprise Systems

There are a lot of great sites and blogs out there that have inspiration and guiding principles for public facing products, but not a lot of information on designing for complex, enterprise level systems. Think about complex applications like AWS, Google Cloud, Microsoft Azure... apps that have huge feature sets with a ton of data that can be leveraged by users. How do you design in such a way that allows them to take advantage of this? These designs are often made internally at an organization and not shared publicly. It would be nice to have a lesson or course on how to design systems like this.