Seeed has two versions of the board files (not the hardware).
- uses the Mbed structure/libraries
- uses Adafruit libraries and bootloader and the Nordic softdevice.
Mbed has their own BLE library and Adafruit has its own BLE library.
The ArduinoBLE library that is used with the Arduino Nano BLE 33 board is also used with the XIA BLE board that was setup for Mbed.
The Adaftuit BLE library is called with Bluefruit.begin() and is used with the XIAO BLE that is using the Adafruit setup… Programs written for the Mbed setup of the XIAO BLE most of the time do not work with XIAO BLE board using the Adafruit setup.
So when you install your XIA BLE board in the Arduino IDE, you need to decide which board files (and libraries) you want to use: Mbed or Adafruit.