Finally I got working the BLE with this board and mbed version and with ArduinoBLE.h.
Now I’m trying to get it down to sleep and weak up. But I can only find codes for adafruit. (bluefruit.h but nothing for the mbed architecture.)
The ArduinoLowPower.h gives error at translation time, (and warning as well, that it is not compatilbe with the mbed “WARNING: library Arduino Low Power claims to run on samd, nrf52 architecture(s) and may be incompatible with your current board which runs on mbed architecture(s).” - and it really doesn’t work.
Wake up must be external for a pin state change.