I got an Amazfit Bip to use with GadgetBridge just for this reason, to have control over my data. It's definitely not a very sophisticated device, but it track

I got an Amazfit Bip to use with GadgetBridge just for this reason, to have control over my data. It's definitely not a very sophisticated device, but it tracks my heart rate and activity and can track my walking routes if I want it to. And the data never leaves my devices.