It's not exactly 'opt-out', they ask you on first boot or after major upgrades, and you either select "Share with Apple" or "Don't Share with Apple". It's just that the "Share" button is coloured blue so looks more default since it's more prominent (at least on iOS, I think it's basically the same on macOS).
It's not like it's enabled by default and you have to know to go and find the setting to turn it off or anything..
It’s opt-out, but it’s not enabled silently. It’s a pre-ticked checkbox on a screen you have to review when you first setup the machine (and when you do a major version OS upgrade).
IMO that’s quite different to something that’s just silently on by default, and requires you to set an environment variable or run a command to opt out.
On a phone there is no box at all. It's two options to select. The opt-in is highlighted, but there is no "next" button -- you have to select an option.
It’s not really opt-out or opt-in: it’s an explicit, informed choice you have to make when you start up your Mac after first purchase or major upgrade.
Not the OP, but I am not watching a random YouTube video from a random guy to help you prove your point. I can confidently link you some of these that “prove” that the Earth is flat.
It's not like it's enabled by default and you have to know to go and find the setting to turn it off or anything..