Hello, Lead
Thank you for using our theme.
1/ Theme update should not cause such a problem, because these pages are independent of the theme. Please go WooCommerce > Settings > Advanced > Page setup > select Cart and Checkout pages.
2/ You can enable product categories via Appearance > Menus > Screen options, but there is no option to dynamically add them to menu.
3/ Please read about coupons in the documentation of WooCommerce plugin – https://woocommerce.com/document/coupon-management/
Kind Regards,
8theme team