Look, I'm an idiot. I know that, you know that, and the man on the moon knows that. Let's not get into why I'm an idiot; let's just accept that I have my peculiarities and you have yours. My idiocy is a quest to make sure all my portable electronics can recharge using USB-C. Modern smartwatches are tiny and they do a lot. As a consequence, their battery life is generally poor. The industry's…
The FOSS app GadgetBridge, has a number of supported smartwatches.
Supported watches can sync your health, activity, GPS, heart, O2, sleep data to GadgetBridge locally on your phone, instead of sending it online to who knows where.
May need to use the watches app to set it up, but then all happens locally.