jQuery-ui bug with dd. MM yy date format

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.14.1/jquery-ui.min.js"></script>
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/jqueryui/1.14.1/themes/base/jquery-ui.min.css">
<p>Date: <input type="text" id="datepicker"></p>

JavaScript

var bookable_date=["Fri Apr 9 2021", "Sat Apr 10 2021", "Tue Apr 13 2021", "Wed Apr 14 2021", "Thu Apr 15 2021", "Fri Apr 16 2021", "Sat Apr 17 2021", "Tue Apr 20 2021"];

$(document).ready(function() {

  
	$( "#datepicker" ).datepicker({
  	dateFormat: 'dd. MM yy',	
    defaultDate: bookable_date[ 0 ],
		minDate: bookable_date[0],
		maxDate: bookable_date[ bookable_date.length - 1 ],
    beforeShowDay: function( date ) {
    		console.log(date)
					var formatted_date = $.datepicker.formatDate( 'dd. MM yy', date);

					if ( is_date_available( formatted_date ) ) {
						return [true];
					} else {
						return [false];
					}
    },
    dayNamesShort: ["Su", "Mo", "Tu", "We", "Th", "Fr", "Sa"],
  });

})


function is_date_available( formatted_date ) {
	console.log(formatted_date);
	return bookable_date.includes( formatted_date );
}