While I have many issues with the new file systems as well, it is difficult to justify blaming it for Steam not running. Steam for Mac had never ran with case sensitive file systems since its inception, and Valve continuously refused to fix this despite numerous user complaints. This is hardly Apple’s fault.

I was saying this almost 10 years ago with various applications blowing up on case sensitive HFSX, and not really getting very good reasons why. And it's not just a few developers, they were all telling me case sensitivity on macOS is a problem. They'd get things working with one build, and a new dev build would bust their app but only on a case sensitive file system, not case insensitive. So the fact it's 2018 and this is still going on with APFS? shrug It doesn't surprise me one bit, even though I don't understand why it's still a problem. Two different file systems, same problem. Sounds like Apple just doesn't really care to properly support or test case sensitivity, their own test suite doesn't catch problems in the real world?