//給定$rowpage[][]二維陣列///////
while($rowpage[]=$result->fetch_array(MYSQLI_ASSOC)){
}

.........

for($i=$min;$i<$max;$i++){
echo "<div class='card'>";
echo "<h5 class='card-header'>【".$rowpage['留言編號']."】".$rowpage['姓名']."</h5>";
echo "<div class='card-body'>";
echo "<h5 class='card-title'>".$rowpage['日期時間']."</h5>";
echo "<p class='card-text'>".$rowpage['留言']."</p>";
echo "</div></div>";
}