>I always find it strange when OS updates affect apps in this way. It just shouldn't happen. It reminds me of when Linus preaches that "the kernel should never break userspace". Why would a OS update suddenly cause the Mail app -- developed by the same company as the OS, for what it's worth -- to have these strange (and catastrophic) data syncing issues?
It's doesn't "suddenly" cause the existing Mail app to break.
It's the new version of the Mail app that breaks -- for reasons not having to do with the rest of the OS.
macOS, as an OS, is not just the kernel, SDK, and GUI libs, and tooling: it's rather a distro that includes regular apps like Mail, Safari, Notes, etc.
If it was OS caused, it would affect others apps too.
It's doesn't "suddenly" cause the existing Mail app to break.
It's the new version of the Mail app that breaks -- for reasons not having to do with the rest of the OS.
macOS, as an OS, is not just the kernel, SDK, and GUI libs, and tooling: it's rather a distro that includes regular apps like Mail, Safari, Notes, etc.
If it was OS caused, it would affect others apps too.