How does Xiaomi Watch S3 stay connected to the Mi Fitness App?

Please set the Mi Fitness App as a whitelist and lock it to run in the background. The phone's Bluetooth will not be turned off, and it will remain connected within the Bluetooth connection distance between the watch and the phone.
The setting methods vary for different mobile phone models. Please go to the [Mi Fitness] app >> [Device] >> enable [Background running permissions] and follow the specific setting methods and prompts for operation.