Designing Data Intensive Applications (DDIA)[1] is a great introductory book for such things. It covers a broad number of system design topics, and you can then go into detail for stuff that interests you.

Other than that, several companies (such as Uber) operating on a large scale maintain engineering blogs.

[1] https://dataintensive.net/

You can practice the mindset by writing a toy solution for the problem, then listing the reasons why you consider your solution just a toy. This develops a fundamental skill of engineering, which isn't understanding whether a system will fail (it will always eventually fail, even if the first reason is that the sun explodes), but rather when and how it will fail. You can make a whole career out of pulling on that thread.

(I worked at Google with Bob in the mid-2000s. I might have interacted with him once or twice on the internal Java and Guice mailing lists, but never met him in person. He was supremely helpful and knowledgeable, and I admired him from a distance.)