It is a common practice by Apple nowadays that they add always add wallpaper to new version of iOS and macOS. Same happened with iOS 12 and macOS Mojave. Apple has added some nice wallpapers to iOS 12 and macOS Mojave.
Like lot of users, if you wish to set these wallpapers on your iPhone/iPad/iPod Touch and Mac running on older versions, good news is that they are available for download.
Download iOS 12 New Wallpaper
If you happen to own iOS device like iPhone, iPad or iPod Touch and want to set the iOS 12 wallpaper as default, you must download the wallpaper first.
We recommend to download it on your iOS device to avoid the task to transferring it later using computer. You can download iOS 12 wallpaper from here.
Download macOS Mojave New Wallpaper
As for macOS Mojave is concerned, Apple has basically added four wallpapers in this latest macOS 10.14. You can download macOS Mojave wallpapers from here.
Let us know how these wallpapers look on your device.