[theshrike79]

Naturally the server needs to know things.

If you want it to, for example, summarise your HRV or menstrual cycle you can't anonymise it or you don't have any data to analyse. It'd be just "wink wink nudge nudge" with zero context.

[simjnd]

Of course, but the iPhone could send slightly altered data to avoid fingerprinting (tweaking age / weight / height slightly) like browsers do with sensors.

Some data could outright be replaced (names, etc) and swapped back on device.

It couldn't do it with ALL the data (eg. calendar data needs to be accurate) but just because you need to give context doesn't mean sacrificing privacy.

Everything would go through an Apple proxy before reaching a theoretical 3rd-party provider.

These wouldn't provide privacy GUARANTEES but could make it reasonably difficult and expensive to fingerprint?