/**
 * @snippet       WooCommerce Holiday/Pause Mode
 * @how-to        Get CustomizeWoo.com FREE
 * @sourcecode    https://businessbloomer.com/?p=20862
 * @author        Rodolfo Melogli
 * @testedwith    WooCommerce 3.5.1
 */
// Trigger Holiday Mode
add_action ('init', 'bbloomer_woocommerce_holiday_mode');


// Disable Cart, Checkout, Add Cart
function bbloomer_woocommerce_holiday_mode() {
   remove_action( 'woocommerce_after_shop_loop_item', 'woocommerce_template_loop_add_to_cart', 10 );
   remove_action( 'woocommerce_single_product_summary', 'woocommerce_template_single_add_to_cart', 30 );
   remove_action( 'woocommerce_proceed_to_checkout', 'woocommerce_button_proceed_to_checkout', 20 );
   remove_action( 'woocommerce_checkout_order_review', 'woocommerce_checkout_payment', 20 );
   add_action( 'woocommerce_before_main_content', 'bbloomer_wc_shop_disabled', 5 );
   add_action( 'woocommerce_before_cart', 'bbloomer_wc_shop_disabled', 5 );
   add_action( 'woocommerce_before_checkout_form', 'bbloomer_wc_shop_disabled', 5 );
}
// Show Holiday Notice
function bbloomer_wc_shop_disabled() {
        wc_print_notice( 'SKLEP W FERIE NIECZYNNY :)', 'error');

}
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
<br />
<b>Warning</b>:  Cannot modify header information - headers already sent by (output started at /home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-content/themes/twentytwenty/functions.php:1) in <b>/home/klient.dhosting.pl/paweltuga/pacynki.dfirma.pl/public_html/wp-includes/rest-api/class-wp-rest-server.php</b> on line <b>1378</b><br />
{"id":1,"name":"pawel","url":"http:\/\/wordpress.example","description":"","link":"https:\/\/pacynki.pl\/author\/admin\/","slug":"admin","avatar_urls":{"24":"https:\/\/secure.gravatar.com\/avatar\/3af00320b9440e9448c36711e459929f?s=24&d=mm&r=g","48":"https:\/\/secure.gravatar.com\/avatar\/3af00320b9440e9448c36711e459929f?s=48&d=mm&r=g","96":"https:\/\/secure.gravatar.com\/avatar\/3af00320b9440e9448c36711e459929f?s=96&d=mm&r=g"},"meta":[],"woocommerce_meta":{"activity_panel_inbox_last_read":"1608290832384","activity_panel_reviews_last_read":"","categories_report_columns":"","coupons_report_columns":"","customers_report_columns":"","orders_report_columns":"","products_report_columns":"","revenue_report_columns":"","taxes_report_columns":"","variations_report_columns":"","dashboard_sections":"","dashboard_chart_type":"","dashboard_chart_interval":"","dashboard_leaderboard_rows":"","homepage_stats":"","android_app_banner_dismissed":""},"_links":{"self":[{"href":"https:\/\/pacynki.pl\/wp-json\/wp\/v2\/users\/1"}],"collection":[{"href":"https:\/\/pacynki.pl\/wp-json\/wp\/v2\/users"}]}}