Is this Settings > Data Controls > "Improve the model for everyone" or is there a "disallow training" somewhere else?

presumably its default behavior will vary depending on your user subscription or if your account belongs to an organization (Business, Enterprise, Edu?).

Yes that's what I was referring to. I'm a non paid user but I did briefly pay for a consumer subscription before. Not sure what region I'm assigned to as I'm in China and always access through a VPN.