There’s some hope here. I originally thought Blizzard had moved to a version of XCode that was too new to target older OSes, but chipzz dug deeper and found the most likely reason why this broke. If this is all that’s truly wrong, it’s a super easy fix on Blizzard’s end. It’s just a matter of them noticing chipzz’s post and getting permission to push a macOS patch out (normal procedure for macOS patches is that they don’t get to go out unless there’s a Windows patch cycle scheduled, but for critical issues like this that may not apply this time).