I was wondering if you are considering to integrate smart watches into your supported devices list.
I’ve been considering to get (any) one for a while now. But when considering the privacy consequences that come with a stock device I always neglected the idea.
Also a refurbished one would probably do as well.
I use the Garmin Connect app with my Garmin watches (currently Fenix 6S Solar, several others previously). It has always worked fine with IodéOS, and with other Open Source ROMs (/e/OS, lineage4microg)
I used for a while the original Zepplife app with my miband5.
It’s possible to configure it so that it stores data only locally (but you should trust it since it is closed source).
The application connects continuously to the Internet, if you block it, it wouldn’t work.
You can block only selected api, but finding the right configuration is complicated.
That’s why I decided to switch to gadgetbridge.