Is it possible to find blood oxygen level from smartphone camera?

It is certainly possible, but not as accurate as pulse oximetry.

You could look at these: https://ieeexplore.ieee.org/document/7145228 https://dl.acm.org/doi/abs/10.1145/3360725

I would guess not, since Samsung used to include a specific blood oxygen sensor right next to the phone camera. If they could do it with one sensor, they wouldn't need to do that.