We've been considering privacy manifests to be an iOS-only issue so far, but while Required Reason APIs explicitly list every platform but macOS, https://developer.apple.com/support/third-party-SDK-requirements/ doesn't actually specify anything about platform, and privacy manifests are for any platform—they just don't need NSPrivacyAccessedAPITypes on macOS (per the note on that page).

In practice, https://developer.apple.com/support/third-party-SDK-requirements/ doesn't list any of our macOS plugin implementations, and it doesn't list FlutterMacOS, so it's effectively iOS-only for us right now. However, adding an empty manifest to the engine on macOS would be easy, and would future-proof us against having to do work later that would need to percolate through the release channels (or require a cherry-pick), and should be harmless even if never needed. Given that, we should consider just going ahead and doing that.

(Signing might be more complex to do? I'm not clear on that part of the pipeline.)

/cc @cbracken @jmagman