Apple only disabled the pulse ox sensor on watches they sold, distributed, or replaced after the ruling. I don't think Apple disabled a working pulse ox sensor on anyone's watch other than repairs.
And only in the USA, as far as I understood. You could but the same watch in Canada and the pulseox worked.
Correct. The sensor was the same in the Series 10 and Ultra 2 because in territories outside the US it worked just fine. Similar to how Samsung offer blood pressure readings in certain countries but in others the function is blocked at the software level.