You can do this with Javascript now. This link shows how to disable weekends. 

You can use the below modified code to also grey out your holidays. You will use "myDate" as the CSS field. You will need to add your holidays to the holidayList.
 

$(document).ready(function () {
/*Limits date selection exclude weekends and holidays*/

//Add your holidays in string format. All holidays must be in holidayList.
const holidayList = ['2024-7-5','2024-8-14'];

// Checks if date is a holiday or a weekend
function isCorrectDate(n) {
    var t = n.getDay();
    var c = n.getFullYear() + "-"+(n.getMonth()+1)+ "-"+n.getDate();
    var h = holidayList.includes(c)
    return (t!=0 && t!=6 && h==false);
  }
  
//Sets up date picker with greyed out weekends and holidays.
  function checkDate(n) {
    return[isCorrectDate(n),""];
  }
  function checkField(input, inst) {
    if ($(input).closest('li').hasClass('myDate')) {
      $(input).datepicker("option", {beforeShowDay: checkDate});
    }
  }
  $.datepicker.setDefaults( {beforeShow: checkField} );
  window.Parsley.addValidator('secondsat', {
    validateString: function(value) {
      return isCorrectDate(new Date(value));
    },
    messages: {
      en: 'Not valid date.'
    }
  });
  
  $('.myDate input').attr('data-parsley-secondsat','');
          
});