They do show that: https://www.flyzipline.com/technology (scroll down, it first shows the thing that it drops, rather than the drone itself.)

Lots of CGI and notices about "simulated" though. The videos that appear to maybe be real show something that does have wings, but looks too small/light/thin to carry much around.

The ones they are currently using in Africa are normal drone planes. They drop their payload without stopping though, so the payload has to be packed securely and nothing that can break easily. So it's used for medical supplies. This what Mark Rober's video was about.

If they were to create a drone that can deliver arbitrary packages, then it needs to be able to lower a package safely. That's what those renders are, they show a typical multi-rotar drone with small wings. So it can stop and lower a package. I don't think there's any real footage of these yet.

He shows the proposed new model in that video too though, not just the drone planes.

The concept of a fixed-wing VTOL UAS is well-tested, though. They’re not as simple as a quad or a “native” fixed-wing, but well within reach of a motivated hobbyist.

Came here to say that (i think their operations in Africa are quite impressive) but it seems as their "Zips" are a different kind of breed and more like a drone than a plane.