This is in fact an PHP 7.3 upgrade compatibility with older PHP scripts.
This is a quick fix for CodeIgniter.
Message: The each() function is deprecated. This message will be suppressed on further calls
Filename: core/Security.php | Line: 272
On line 272, of file application/system/core/Security.php there should be an ‘while’ with a ‘each’.
Make the following changes
//while (list($key) = each($str)) foreach($str as $key=>$str_values)