O2 sensor

I have had my watch for a while now and was curious about the LED lights and asked on line and one reason was the 02 sensor to detect the saturation of oxygen in the blood. I remember trying it out for a week out two when I was getting health, running a lot and training. Recently I looked for it again and it’s gone. I saw in the health app it was removed. I tried to find it and even went to You tube They not are saying the 02 sensor was never an option for the watch I have. But that’s impossible since I remember using it. Also the led lights on the back used to be SUPER BRIGHT and there was three or four of them. Now I see one thing green one. WTH!!!!!