why does "STRING".getBytes() work different according to the Operation System
You are not specifying a charset when calling getBytes(), so it uses the default charset of the underlying platform (or of Java itself if specified when Java is started). This is stated in the String documentation:
public byte[] getBytes()
Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
getBytes() has an overloaded version that lets you specify a charset in your code.
public byte[] getBytes(Charset charset)
Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.