Wishlist

This app has no admin interface — it is configured entirely from the theme editor.

Activate the app embed. It is off by default, and without it the storefront loads no wishlist code at all. Theme settings → App embeds → Wishlist.
Point it at your product cards. In the embed settings, set the product card selector — .card-wrapper on Dawn, .product-item on Focal-derived themes. Turn on console logging to check how many cards it matched.
Add the wishlist page. Create a page, create its template, then add the Wishlist grid block.

The storefront reads and writes the wishlist at /apps/wishlist, which Shopify signs before forwarding it here. Requests without a valid signature, or for a customer other than the signed-in one, are refused.