How to prevent selection of weekends in date picker?

We can provide no weekend function into the date picker option. Please follow next steps:

1. Use next Custom CSS and add them to Customizer > Additional CSS field:

.ui-datepicker-week-end {
    display: none !important;
}

2. Also, make sure to add next JS into Custom JS field in Customizer > General Settings:

const picker = document.getElementById('date');
picker.addEventListener('input', function(e){
  var day = new Date(this.value).getUTCDay();
  if([6,0].includes(day)){
    e.preventDefault();
    this.value = '';
    alert('Weekends not allowed');
  }
});

3. Than edit line 444 in bt_cost_calculator.php file, located in \wp-content\plugins\bt_cost_calculator folder on your site :

$output .= '<div class="btQuoteItem' . $m_date . '"><input type="text" class="btContactDate btContactField" placeholder="' . $date_text . '"></div>';

replace with next line:

$output .= '<div class="btQuoteItem' . $m_date . '"><input type="text" class="btContactDate btContactField" id="date" placeholder="' . $date_text . '"></div>';