No, it’s documented API. It’s either because it doesn’t actually work as documented, or because the other applications’ developers are lazy.

https://developer.apple.com/documentation/security/password_...

Your link is for app development, not web.

The comment claims Safari, an app, has exclusive access to system features, my comment shows how other apps have access to the same features. The web has nothing to do with it.

I see that now after re-reading. You meant the other browser developers could add this. I first took it as saying websites could add it with some input attribute. My mistake.