Turning on Full compiler warnings give a number of these types of warnings

..Documents\Arduino\libraries\ArduinoBLE\src\utility\HCI.cpp:472:41: warning: variable length array 'txBuffer' is used [-Wvla]
   uint8_t txBuffer[sizeof(pktHdr) + plen];

These warnings from the library make it difficult for the library user to monitor the compilation output for important warnings for problems in their own code.

Please fix or suppress these warnings if possible.