There is now an instruction for the Kingwear KW88 Pro, an 80 USD Android watch, to install Linux AsteroidOS on it. As for the Linux PinePhone, it should be possible to run software for ANT+ and BLE sensors on the Kingwear KW88 Pro Linux watch. Needs to be tested.
According to the Asteroid IRC chat, the Bluetooth stack of the Kingwear KW88 Pro is a mess. I suggest to use another watch, if Bluetooth is important, for instance: