PDO statement, quotes are stored as? - php

Question

So, I'm really new to PDO, and I was trying some stuff and practicing it, and happens that I became really confuse about what is happening to my database once I'm trying to insert some special characters with this code below:
<?php
$post_cat = 4;
$post_title = "TESTING";
$post_author = "Test";
$post_image = "test_image.png";
$post_content = "“Luo Changan, I grant you five breaths’ time. Show me whether you’re actually such a ‘person’ as you say, or a dog that would ‘beg to surrender!’”";
$post_tags = "novel, mga, chinese novel";
$ID_post_stat = 2;
$pdo = new PDO("mysql:charset=utf8mb4;hostname=localhost;dbname=cms;", "root", "");
$stmt = $pdo->prepare('INSERT INTO posts (ID_post_category, post_title, post_author, post_image, post_content, post_tags, ID_post_status) VALUES (?, ?, ?, ?, ?, ?, ?)');
$stmt->bindParam(1, $post_cat);
$stmt->bindParam(2, $post_title);
$stmt->bindParam(3, $post_author);
$stmt->bindParam(4, $post_image);
$stmt->bindParam(5, $post_content);
$stmt->bindParam(6, $post_tags);
$stmt->bindParam(7, $ID_post_stat);
$stmt->execute();
/* data stored:
+------------------+------------+-------------+----------------+-----------------------------------------+---------------------------+----------------+
| ID_post_category | post_title | post_author | post_image | post_content | post_tags | ID_post_status |
+------------------+------------+-------------+----------------+-----------------------------------------+---------------------------+----------------+
| 4 | TESTING | Test | test_image.png | ?Luo Changan, I grant you five breaths? | novel, mga, chinese novel | 2 |
| | | | | time. Show me whether you?re actually | | |
| | | | | such a ?person? as you say, or a dog | | |
| | | | | that would ?beg to surrender!?? | | |
+------------------+------------+-------------+----------------+-----------------------------------------+---------------------------+----------------+
*/
?>
I was looking for answers for why this characters (“ ‘ ’ ”) are not being stored on database and are replaced with (?) instead, I had tried to change the table and column to UTF8 as I had read some answers from the community, but it don't seems to make difference, its working fine with (áéíóú) though. Thanks in advance!
as suggested by Madhur Bhaiya, I had tried again to check on it charset, even aplied charset=utf8mb4 to my PDO DSN what helped me alot instead of using utf8_decode or utf8_encode to each string, and it is indeed all set to UTF8 already, so I guess that this kind of characters like curly quotes aren't supported for this charset, then how can I solve this?