Typical usage of blood glucose monitoring (by diabetics) is simultaneously safety critical, and only borderline good enough accuracy. There's a standard metric for accuracy here, MARD (mean absolute relative difference).
There is a long history of companies promoting themselves to investors as having working noninvasive glucose monitoring technology, which, if you look at the actual accuracy scores, is only moderately correlated with glucose, nowhere close to the accuracy required. If Apple ships a noninvasive glucose monitor with an MARD of 20, the primary effect will be to set a trap for the stupid: diabetics will attempt to use it to save money, since it will be much cheaper than using real CGMs (which are consumable), and people who try to do this will die.
There is a long history of companies promoting themselves to investors as having working noninvasive glucose monitoring technology, which, if you look at the actual accuracy scores, is only moderately correlated with glucose, nowhere close to the accuracy required. If Apple ships a noninvasive glucose monitor with an MARD of 20, the primary effect will be to set a trap for the stupid: diabetics will attempt to use it to save money, since it will be much cheaper than using real CGMs (which are consumable), and people who try to do this will die.