The gift card page is not in your menu. When someone buys a Shopify gift card, Shopify emails the recipient a link to it. The page shows the value, the code, a QR code the front desk can scan, an Apple Wallet button where Shopify provides a pass, and your store name and logo.
To see it, open Products, open your gift card product, and choose Preview gift card.
Service gift cards sold through your booking provider are a different thing: the Gift card band section links to them with the Gift cards page address from Theme settings → Booking. See Gift cards.