Euro (€) symbol in php array displayed as question mark

I have a very annoying problem with the euro symbol in my PHP-array.
I would like to split strings of different lengths by every character into arrays.
E.g.: “Hi guys” ==> array(“H”, “i”, ” “, “g”, “u”, “y”, “s”)

This works great except with the € symbol.
As soon as a “€” is in the string it is output as “�”. I have already tried a lot, but unfortunately I can’t get any further.

UTF-8 is set as default-charset in php.ini.

Do you have a tip for me?

This is a simple example:

<?php 
  $euro = "€";
  $split = str_split($euro);
  echo $split[0]; // Ouput in browser: �
?>

Thanks a lot!

I have already researched for hours on the Internet and tested the various functions…