Since Porto theme has there owned gallery markup that reason the quick view feature is not working properly with the "product gallery slider" . so we need to override the ajax function only for the quick view mode.to do this just copy the code from below and paste it into your child-theme/functions.php or create a custom plugin to add this code.

porto-theme-quickview.php

<?php 
add_action( 'init', 'cix_new_hooks');
function cix_new_hooks(){
remove_action( 'wp_ajax_porto_product_quickview', 'porto_product_quickview' );
remove_action( 'wp_ajax_nopriv_porto_product_quickview', 'porto_product_quickview' );

add_action( 'wp_ajax_porto_product_quickview', 'cix_porto_product_quickview' );
add_action( 'wp_ajax_nopriv_porto_product_quickview', 'cix_porto_product_quickview' );
}

function cix_porto_product_quickview() {
    //check_ajax_referer( 'porto-nonce', 'nonce' );
 
    // phpcs:disable WordPress.Security.NonceVerification.NoNonceVerification
    global $post, $product;
    $post    = get_post( (int) $_REQUEST['pid'] );
    $product = wc_get_product( $post->ID );
    if ( post_password_required() ) {
        echo get_the_password_form();
        die();
        return;
    }
    porto_woocommerce_add_js_composer_shortcodes();
    ?>
    <div class="quickview-wrap quickview-wrap-<?php echo esc_attr( $post->ID ); ?> single-product<?php echo ' product-type-' . esc_attr( $product->get_type() ); ?>">
        <div class="product product-summary-wrap">
            <div class="row">
                <div class="col-lg-6 summary-before">
                    <?php
                    get_template_part('woocommerce/single-product/product-image');
                    
                    ?>
                </div>
                <div class="col-lg-6 summary entry-summary">
                    <?php
 
                    do_action( 'woocommerce_single_product_summary' );
 
                    if ( ! isset( $_REQUEST['variation_flag'] ) || ! $_REQUEST['variation_flag'] || 'false' == $_REQUEST['variation_flag'] ) :
                        ?>
                    <script>
                        <?php
                        $suffix               = defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min';
                        $assets_path          = esc_url( str_replace( array( 'http:', 'https:' ), '', WC()->plugin_url() ) ) . '/assets/';
                        $frontend_script_path = $assets_path . 'js/frontend/';
                        ?>
                        var wc_add_to_cart_variation_params = 
                        <?php
                        echo array2json(
                            apply_filters(
                                'wc_add_to_cart_variation_params',
                                array(
                                    'wc_ajax_url' => WC_AJAX::get_endpoint( '%%endpoint%%' ),
                                    'i18n_no_matching_variations_text' => esc_js( __( 'Sorry, no products matched your selection. Please choose a different combination.', 'woocommerce' ) ),
                                    'i18n_make_a_selection_text' => esc_js( __( 'Please select some product options before adding this product to your cart.', 'woocommerce' ) ),
                                    'i18n_unavailable_text' => esc_js( __( 'Sorry, this product is unavailable. Please choose a different combination.', 'woocommerce' ) ),
                                )
                            )
                        )
                        ?>
                        ;
                        jQuery(document).ready(function($) {
                            $.getScript('<?php echo porto_filter_output( $frontend_script_path . 'add-to-cart-variation' . $suffix . '.js' ); ?>');
                        });
                    </script>
                    <?php endif; ?>
                </div><!-- .summary -->
            </div>
        </div>
    </div>
    <?php
    // phpcs:enable
    die();
}