How to the pass specific day from cakephp controller to Fullcalendar integrated view file - cakephp

Question

I want to pass the specific day value to that specific month day on fullcalendar interface, so that day(not date only specific day like 'Wednesday') should be color red on calendar. Can anyone help me on this?
public function appointmentCalendar($chamberId=null){
$this->loadModel('ScheduleChember');
$chamberInformation= $this->ScheduleChember->get($chamberId);
$providerId = $this->Auth->user(['id']);
$doctorOffDay = $this->AppointmentScheduleChamberSlots->find('all')->where(['provider_id' =>$providerId, 'schedule_chember_id'=> $chamberId, 'off_day' => 1])->select(['day_name'])->toArray();
$this->set(compact('chamberInformation', 'doctorOffDay'));
}
<h1><?php echo $chamberInformation->name; ?></h1>
<script src='https://cdn.jsdelivr.net/npm/fullcalendar-scheduler#6.1.1/index.global.min.js'>
</script>
<script>
document.addEventListener('DOMContentLoaded', function() {
var calendarEl = document.getElementById('calendar');
var someVariable = <?= json_encode($doctorOffDay) ?>;
var calendar = new FullCalendar.Calendar(calendarEl, {
initialView: 'dayGridMonth',
eventColor: 'red',
headerToolbar: {
start: 'prev',
center: 'title',
end: 'next'
},
events: [
{
title: 'Off Day',
start: '2023-02-08'
},
]
});
calendar.render();
});