Unfortunately, there isn’t an officially-supported way to display content from Builder inside Magento. I’m not very familiar with that platform, but if there’s a way to embed external webpages inside your Magento pages, that’s probably the route you’d want to go.
I do see that one can develop Magento extensions that communicate with external API’s. I don’t know how these extensions can be used, but if they can populate your Magento pages with content from Builder, you could write an extension that pulls data from Builder’s content API in JSON or the GraphQL API. You could even use the HTML API to get server-rendered HTML and inject that onto your page.
One more thing. Your instinct to enable the Magento integration was a sound one, but unfortunately our e-commerce integrations don’t push data from Builder to Magento. For that matter, they don’t pull data from Magento into Builder.
Builder’s e-commerce plugins create custom types corresponding to your external platform’s resources, which you can use when targeting content, previewing content, and using your content as a symbol inside of Visual Editor. Typically, you would write the integration yourself to pull the relevant data from Magento and display it inside of your Builder content. The plugin helps in that.
I’m actually in the middle of overhauling our plugin/integrations documentation, and I will be sure to address this confusion.
I hope that helps clarify things a bit!