Extras can be offered as an upsell in two independent ways on the Cart review page, each its own Client Config toggle (both off by default): "Extras: Show on the Cart Preview Page" shows an inline, auto-scrolling carousel of extras (with left/right arrows) right on the review page; "Extras: Add a Popup on the Cart Preview Page" instead pops up a modal titled "Additional Products" asking "Are you sure you don't want extras?", with the same extras carousel inside it. A store can enable either, both, or neither — if neither is on, extras simply don't appear as an upsell during cart review (you'd still find them on the separate Extras ordering page if that module is enabled). In the current version, clicking an extra in either the banner or the popup does not add it to your cart directly — each card is a link that takes you to the Extras ordering page, where you'd add it from there.