Requires minimum iOS 17.
The bundled images are just meant to be able to quickly try out the app. The point is to use your own images or from a service like Unsplash.
I don't plan to integrate with Unsplash. There is a better way. Save the images you want in the Unsplash app, open the Photos app, go to one of the images, tap the share button, and tap “Make Blurry Wallpaper”.