If this is in there I apologize!
When adding various apps to the Portfolio Instant App, there is the option to use an image URL to load a thumbnail image. I would like to see the ability to create a thumbnail from the content on-the-fly. In a sense, capturing a screenshot of the app and using it as the thumbnail image, as an alternative.
Thanks for the feedback. You can add an image URL to be used as the thumbnail currently, this is available under the Item info when adding or editing items in Portfolio (see image below). We don't have an option to adjust the thumbnail on-the-fly in the app but will look into options to incorporate this into a future update. Until then, you can visit the item details of the specific item you're adding to adjust the thumbnail.