$str = "Array ( [Discord] => Alabros#0001 [Isim] => KULISMTEST [Soyisim] => KULISIM [Numarasi] => 2017857 [Image] =>123 )";
$pattern = "/\[Isim\][\s=>]+([A-Za-z0-9çşöğü\-\.\s]+)\[/i";
preg_match_all($pattern, $str, $matches);
echo $matches[1][0]; //KULISMTEST