The Arduino core for Nano 33 BLE is based on Mbed and can be used in Mbed as library. To achieve this, the Arduino API classes in this core are put in a namespace arduino::
. This causes problems for libraries which include individual includes of Arduino API historically copied into cores for different MCU architecture platforms. The Arduino.h file includes the API files in the right way so in this case replacing #include"Print.h"#include"Print.h"
with #include <Arduino.h>#include <Arduino.h>
in LiquidCrystal.h solves the compilation problem.