First, thanks for the reply. It helps me a lot to understand more about Odoo.
When i try it, i have this error when open my odoo (I restart odoo server with --dev=assets flag)

"The following modules are needed by other modules but have not been defined, they may not be present in the correct asset bundle:
web.CalendarController
web.rpc
The following modules could not be loaded because they have unmet dependencies, this is a secondary error which is likely caused by one of the above problems:
@cng_appointments/js/appointment"

JavaScript file is added on __manifest__.py file

'assets': {
'web.assets_backend': [
'cng_appointments/static/src/js/calendar_restriction.js',
],
}

Hello! I cant provide a screenshot (button disabled) but this is what i have.

<record id="action_appointment_calendar" model="ir.actions.act_window">
<field name="name">Calendario de Citas</field>
<field name="res_model">cng_appointments.appointment</field>
<field name="view_mode">calendar,tree</field>
</record>

<record id="view_appointment_calendar" model="ir.ui.view">
<field name="name">cng_appointments.appointment.calendar</field>
<field name="model">cng_appointments.appointment</field>
<field name="arch" type="xml">
<calendar string="Calendario de Citas" mode="day" date_start="date_start" date_stop="date_end" color="box_id">
<field name="patient_id"/>
<field name="service_id"/>
<field name="box_id"/>
<field name="center_id"/>
</calendar>
</field>
</record>

<record id="view_appointment_calendar" model="ir.ui.view">
<field name="name">cng_appointments.appointment.calendar</field>
<field name="model">cng_appointments.appointment</field>
<field name="arch" type="xml">
<calendar string="Calendario de Citas" mode="day" date_start="date_start" date_stop="date_end" color="box_id">
<field name="patient_id"/>
<field name="service_id"/>
<field name="box_id"/>
<field name="center_id"/>
</calendar>
</field>
</record>

<menuitem id="menu_appointment_root" sequence="1" name="Gestión de Citas"/>
<menuitem id="menu_calendar_appointments"
name="Ver Citas"
parent="menu_appointment_root"
action="action_appointment_calendar"/>

I validate all on appointment form (After select a hour/day and confirm the popup create buttom). But i want the validations on the calendar. I mean, disable click or info the person that center is closed before the popup create button appears. @Sandeep Mishra answer i think works well but i have an error when try it.

Sorry with my english, is not good. Hope you understand what i want :')

Hello matias
thanks for sharing the code this did me help for understanding your need and your problem.
you need to create a separate model named off days in which youre storing dates which are off dates and also passing a method in the calender model whcih will check the date is an off date and pass then show an warning/validation (depends on that youre passing on the offday) that the day with an off day should not be selected/ your string for the off day choosen and also you can create an boolean which will check the saturday sunday off and add those days in the off days model i believe this would help if it doesnt you can still ask me here or ping me here by upvoting i will surely respond you with your need.
Thanks
and yes this is an view (Calender view) adding constraint/validation via js doesnt make sense doing via backend/python does thus do it via python if you have this form on the portal end/website module then you need to create a validation via js.

I try what Sandeep Mishra but i have this error when restart odoo server.

"The following modules are needed by other modules but have not been defined, they may not be present in the correct asset bundle:
web.CalendarController
web.rpc
The following modules could not be loaded because they have unmet dependencies, this is a secondary error which is likely caused by one of the above problems:
@cng_appointments/js/appointment"

Do you have any idea what can this error be?

Hello matias,
the sandeep mishra thing need to be covered in the asset as in the manifest you need to add the file name under the folder with the path given so the compiler will register your file and thus will need compile your code and give you an needed response you needed thus for the sandeep code you need to add that in manifest file which i will give you an example below.
If this doesnt solve your problem give me your whole js code and then give me your whole error in the message thus i can see that and respond you properly with that i have your calender thing code just give me manifest code andf the js code which you have written for the validation feature.
I am providing you the code of the js file register in the manifest below.
Thanks

#This you need to put below the data file in the manifest file
# "assets": {
# "web.assets_frontend": [
# # assets for frontend
# ],
# },