PHP + SQL Dropdown locale issues [duplicate]

I am creating a PHP form, which collects items for a dropdown list from WordPress MySQL database. The database locale is set to utf8mb4_unicode_520_ci and I tried to force this in the code, however, my dropdown list still does not display any Cyrillic characters.

  <div>
    <label for="course_name">Course Name:</label>
    <select id="course_name" name="course_name" required>
        
      <?php
        // Connect to the MySQL database
        mysqli_set_charset($conn, "utf8mb4_unicode_520_ci");
        mysqli_query($conn, "SET collation_connection = 'utf8mb4_unicode_520_ci'");
        $conn = mysqli_connect("host", "user", "password", "database");
        
        // Query to select all course names
        $query = "SELECT post_title FROM wpv1_posts WHERE post_type = 'courses'";
        $result = mysqli_query($conn, $query);
        // Loop through the result set and create options for the dropdown list
        while ($row = mysqli_fetch_assoc($result)) {
          echo "<option value='".$row['post_title']."'>".$row['post_title']."</option>";
        }
        mysqli_close($conn);
      ?>
      

      
    </select>
  </div>

The result in the dropdown at the moment is basically:

I tried forcing the locale through mysqli_set_charset($conn, "utf8mb4_unicode_520_ci"); and mysqli_query($conn, "SET collation_connection = 'utf8mb4_unicode_520_ci'");, as well as doing the same with cp1251_general_cs. This yielded no results.