Skyfill allows you to do fill in the gap in the sky in high-resolution images. I used it for all my own drone panoramas.
Most drones (UAVs) cannot look straight up to photograph the sky above them. As a result, spherical panoramas made with drones tend to have a gap in the sky. Some drones, like my DJI Mavic 2, can fill in this gap automatically while generating a preview. However, when I stitch the photos myself to get a better quality output, there is still that sky gap. I got fed up with having to choose between a nice sky or a nice overall image, so I did what developers do and made my own software: Skyfill.
Thanks to Ork de Rooij for his help getting the pixels right.