Interestingly, newer version Fitbit devices also sport an SpO2 sensor, but they have dragged their feet on enabling direct readings or the expected sleep apnea detection features.

The delay seems to have come from the worry of the perception that it was being used for "diagnosis" of sleep apnea as that would put them in a different category with the FDA. You can imagine how direct access to the SpO2 sensor was a hot topic during the height of the pandemic of a repository illness. In short, the hardware is there, but corporate conservarivism kept it from being used or even exposed to the user.

I've bought a Withings Smart Scale (at that point they were briefly owned by Nokia). The scale is simple, clean, durable, featureful; the companion health app is one of the cleanest/effective specimins of UI I've seen in a while and has tons of integrations. I expect great things here and hopefully less fear about exposing the hardware readings of highly useful sensors.