1. Turn on the synchronization option: Make sure that you have turned on the iCloud synchronization option and enabled it on all devices. If synchronization is not enabled on your device, you will not be able to view the fitness data of other devices.
2. Devices are not connected to the same network: If your devices are connected to different networks, they may not communicate normally. Please ensure that all your devices are connected to the same Wi-Fi network or use the same mobile data.
3. Different versions of the fitness application installed on the device: If different versions of the fitness application are installed on your device, it may cause synchronization problems. Please ensure that the same version of the fitness application is installed on all devices.
4. privacy settings: if the privacy settings of your device prevent the fitness application from synchronizing, please go to settings > privacy > health and make sure that the synchronization function of the fitness application is enabled.
If the above method doesn't solve the problem, you can try logging in to the fitness application again on all devices, or contact Apple technical support for more help.