While this is a likely explanation, and also the first thing that occurred to me, it’s also factually incorrect. I have a bit more skills than the average user so I ran it from the CLI to see what the actual error was:
/Applications/Diablo III/Diablo III.app/Contents$ MacOS/Diablo\ III
2025-02-05 03:12:57.836 Diablo III[28542:13810095] No Info.plist file in application bundle or no NSPrincipalClass in the Info.plist file, exiting
The Info.plist file exists and is indeed lacking this key. It also contains this:
DTPlatformVersion
13.1
DTSDKName
macosx13.1
LSMinimumSystemVersion
10.13