Does Add To Cart Anywhere work on my Facebook or Buy Button sales channels?

Unfortunately, Add To Cart Anywhere only works on the Online Store sales channel.

While the Shopify platform offers different sales channels (see https://apps.shopify.com/categories/sales-channels), it does not provide a way to run apps on most sales channels.

If you have seen any third-party app running on a Facebook channel, for example, it probably is not a native Shopify app but an integration with a standard web application.