php echo 中文显示乱码

mysqli_result Object ( [current_field] => 0 [field_count] => 1 [lengths] => [num_rows] => 1 [type] => 0 ) 1-------------�û����Ѵ���
如何解决之前不这样的，可能是升级7.4后出现的,但是之前的php文件依然正常输出中文，所以应该是这个php代码的问题，是什么问题呢

<?php
header("Access-Control-Allow-Origin: *");
header("Content-type:text/html;charset=UTF-8");
require_once 'token_management.php';

$servername="127.0.0.1";
$username="root";
$password="password";
$dbname="dbname";
// $userid=$_GET['user'];
// $uesrpassword = $_GET['password'];
// $type=$_REQUEST['type'];
$userid='abc123456';
$uesrpassword ='abc123456';
$type='sign';
$conn=mysqli_connect($servername,$username,$password,$dbname);
mysqli_report(MYSQLI_REPORT_ERROR | MYSQLI_REPORT_STRICT);
$token_management = new token_management();
if($type == "sign"){
    $sql = "SELECT userid FROM user WHERE userid = '{$userid}'";
    $result = $conn->query($sql);
    print_r($result);
    echo(mysqli_num_rows($result));
    echo('-------------');
    if (mysqli_num_rows($result) != 0) {
        echo "用户名已存在";
    }else{
        echo '不存在用户名';
        $sql1 = "INSERT INTO user (userid,password) VALUES ('{$userid}','{$uesrpassword}')";
        $result1 = $conn->query($sql1);
        echo("result1");
        print_r($result1);
        $token = $token_management->get_token($userid);
        echo($token);
    }
}
?>

echo iconv("GB2312","UTF-8",'中文');

https://www.cnblogs.com/cyun/p/4146131.html

检测一下PHP代码文件的字符编码是不是UTF-8

1. php .ini相关文件配置
mbstring.internal_encoding=utf-8
mbstring.http_output=UTF-8
mbstring.encoding_translation=On
default_charset = "utf-8"
mbstring.func_overload=6
2.php代码文件是否是utf-8
3.要在html文件里加上
<meta charset="UTF-8">
4.浏览器是否固定了解码