Fatal error: Uncaught TypeError: mysqli_num_rows(): Argument #1 ($result) must be of type mysqli_result, bool

<?php include('header.php'); ?>
    <!-- end header -->
            <?php 
                include("admin/dashboard/dbs/db_conn.php");
                $mr_qry = mysqli_query($conn,"SELECT * FROM moving_text");
                $mr_num = mysqli_num_rows($mr_qry);
                
                if( $mr_num > 0)
                {
                $mr_row = mysqli_fetch_array($mr_qry);
                echo "
                    <div class='col-md-12'  style='background:#FF8333;'>
                        <marquee style='color:black; font-weight:bold; font-size:20px; padding:5px;'>$mr_row[message]</marquee>
                    </div>
                ";
                }
            
            ?>  

I don’t understand my it is showing this error. Please could anyone help me out in this and solve this so that it will work

I tried alot of things to change the code but it doesn’t seems to work
please anyone can solve this