unexpected route problem

What are you new to? In php?

In the first example, the handler is specified as a string. In this case, the class will be checked for the existence of a namespace, and if it is not found, the default namespace will be added.

In the second example, you specify the handler as a string, where you declare the class name directly. If you don't specify a namespace or don't import, the current namespace will be used.
Current namespace is Config.

PHP Code:

namespace Config;

use Namespace\Example2; 

$routes->get('example1', [Example1::class, 'index']); // \Config\Example1
$routes->get('example2', [Example2::class, 'index']); // \Namespace\Example2
$routes->get('example3', ['\Namespace\Example3', 'index']); // \Namespace\Example3

$routes->get('example4', '\Namespace\Example4::index'); //  \Namespace\Example4
$routes->get('example5', 'Namespace\Example5::index'); //  \App\Controllers\Namespace\Example5 


Thank you for explaining in such a manner.
the problem is solved