I have taken the original nRF52 DK app you reference in your Unofficial example apps
Example implementation UART over BLE section and updated it to work on an iOS iPhone.
The repository is located at:
https://github.com/AllyTechEngineering/flutter_reactive_ble_nrf52_uart
I have not tested on an Android device yet. Feel free to use it.
I have taken the original nRF52 DK app you reference in your Unofficial example apps Example implementation UART over BLE section and updated it to work on an iOS iPhone. The repository is located at: https://github.com/AllyTechEngineering/flutter_reactive_ble_nrf52_uart I have not tested on an Android device yet. Feel free to use it.