What are the practices and methodologies for synchronizing multiple projects?

Question

Project management

Suppose an organization has thousands of information systems connected to thousands of network nodes using various technologies that provide millions of services. What methods and practices do you know of technical synchronization between systems, business processes when one of them changes?
Example (contrived) - we change the whole mail system (not just one server) and another 100 systems similar in scale to it, how to synchronize this activity with a thousand other information systems working with it?
After. There is a portfolio of technical projects with a three-year implementation horizon. Throughout the entire period, hundreds of different information systems are integrated with it. How to respond in a timely manner to changes in systems integrated with them, what are the practices for accounting for such changes?
What would you recommend to read on this topic?

Answer 1

There is, for example, https://www.scaledagileframework.com/
https://www.scrum.org/resources/online-nexus-guide
You can also search for project interdependencies and there are many articles about managing dependencies between projects. There is probably something like this in some PMBok