The USPTO has published a patent for 'three-wavelength pulse oximetry', filed by Garmin in 2020. The new style of sensor could make its way into commercially-available smartwatches, although Garmin is expected to launch the Forerunner 255 and Forerunner 955 series before that happens.
https://www.notebookcheck.net/Garmin-patent-revealed-with-aim-of-improving-SpO2-monitoring-in-smartwatches.621254.0.html