Okay, risolto:
codice:
$date_list = "";
$sql = "SELECT start, end FROM calendario ORDER BY id ASC";
$result = $link->query($sql);
while($row = $result->fetch_assoc()) {
$start = $row["start"];
$end = $row["end"];
$data_in = new DateTime($start);
$data_out = new DateTime($end);
$diff = $data_out->diff($data_in);
$diff->days;
$create_date = [];
for ($i=1;$i<=$diff->days;$i++) {
$data_in->add(new DateInterval('P1D'));
$create_date[] = $data_in->format('Y-m-d');
$date_list .= implode(",", $create_date) . ",";
}
}
$cutchar = 10;
$date_list = substr($date_list, $cutchar);
$date_list = implode(',', array_unique(explode(',', $date_list)));
$date_list = str_replace("\"","",$date_list);
$date_list = str_replace(",","','",$date_list);
$date_list = str_replace("-","/",$date_list);
$date_list = "disabledDates: ['" . $date_list . "'], formatDate:'Y/m/d',";
echo $date_list;