Creation of dynamic property DateInterval is deprecated in PHP 8.2+ but i can't refactor Datetime Class

I don't know how to solve this problem. I have the following function in my project:

public static function getTimeAgo($datetime, $full = false) {
    $now = new DateTime;
    $ago = new DateTime($datetime);
    $diff = $now->diff($ago);

    $diff->w = floor($diff->d / 7);
    $diff->d -= $diff->w * 7;

    $string = array(
        'y' => 'ano',
        'm' => 'mes',
        'w' => 'semana',
        'd' => 'dia',
        'h' => 'hora',
        'i' => 'minuto',
        's' => 'segundo',
    );
    foreach ($string as $k => &$v) {
        if ($diff->$k) {
            if($k == 'm') {
              $v = $diff->$k . ' ' . $v . ($diff->$k > 1 ? 'es' : '');
            } else {
              $v = $diff->$k . ' ' . $v . ($diff->$k > 1 ? 's' : '');
            }
        } else {
            unset($string[$k]);
        }
    }

    if (!$full) $string = array_slice($string, 0, 1);
    return $string ? implode(', ', $string) . ' atrás' : 'agora';
}

Variables $diff->w and $diff->d are dynamic properties from the Datetime class which I don't have access to refactor, naturally. What should I do in this case to keep my code in conformity with PHP 8.2+ standards now ?

You can use get_object_vars to convert DateInterval to array. Or you can cast it to array.

$diff = get_object_vars($now->diff($ago));
$diff['w'] = floor($diff['d'] / 7);
$diff['d'] -= $diff['w'] * 7;
// ... rest of your code modified to work with array instead of DateInterval object

This should work too:

$diff = (array) $now->diff($ago);
$diff['w'] = floor($diff['d'] / 7);
$diff['d'] -= $diff['w'] * 7;
// ... rest of your code modified to work with array instead of DateInterval object