What you'll find, when you get done reading, is that you are using an obsolete library. The write() method of the Print class is pure virtual. That means that any class, like LiquidCrystal_I2C, that derives from the Print class MUST implement write() AND must implement it with the proper signature. The write() method is no longer void. It is now size_t, and must return a value. The obsolete library you are using has the wrong signature for the write() method. It's a two line code change to fix it.