PHP array to jQuery array ” Uncaught SyntaxError: Unexpected token < "

To change choices depending on what an user selected in another input/select, you need to use the WP AJAX API.

In your functions.php, use wp_localize_script() to get AJAX url available on front-end and define an AJAX action callback

function mytheme_custom_scripts() {
    if ( is_page('Support') ) {
        $scriptSrc = get_stylesheet_directory_uri() . '/js/freshdeskdata.js';
        wp_enqueue_script( 'myhandle', $scriptSrc , array(), '1.0',  false );
        wp_localize_script( 'myhandle', 'mydata', array( 'ajaxurl' => admin_url('admin-ajax.php') ) );
    }
}
add_action( 'wp_enqueue_scripts', 'mytheme_custom_scripts' );

function get_choices() {
    $main_category = $_POST['main_category'];
    $choices = []; // todo: get choices here
    wp_send_json_success($choices); // send data with success code and die
}
add_action('wp_ajax_get_choices', 'get_choices'); //back-end
add_action('wp_ajax_nopriv_get_choices', 'get_choices'); //front-end

Then in your script make an AJAX call to get the choices

jQuery(function ($) {
    $(document).ready(function() {  
        $("#main-category").on('change', function() {
            $.post(mydata.ajaxurl, { // mydata has been created by the wp_localize_script function
                action: 'get_choices',
                main_category: $("#main-category").val()
            }, function (response) {
                console.log(response)
                // todo: display new choices
            })
        });
    });
});