Array and string offset access syntax with curly braces is deprecated

https://www.w3docs.com/snippets/php/array-and-string-offset-access-syntax-with-curly-braces-is-deprecated.html

Strings may also be accessed using braces, as in $str{42}, for the same purpose.

PHP: How to get characters of string one by one

https://stackoverflow.com/questions/23405616/php-how-to-get-characters-of-string-one-by-one

Warning Internally, PHP strings are byte arrays. As a result, accessing or modifying a string using array brackets is not multi-byte safe, and should only be done with strings that are in a single-byte encoding such as ISO-8859-1.