This App simply allows you to choose two different Wallpapers for your phone - one for the regular "Light" mode and one for Dark Mode. Then every time the System theme changes so does your Wallpaper - just with certain Wallpapers in iOS13 or iOS14.

The App works by using a customizable a Live-Wallpaper. It also allows you to easily share your Wallpapers from other Apps (like the Gallery) with Darkinator.

Furthermore with you are using an older Android Phone which doesn't support the Dark System Theme in Android 10.0 - no problem. For Android 78 and 9 I have created a custom quick settings tile that allows you to enable Darkmode. It even works with certain 3rd party Apps. For Android 6 devices you have the option to Toggle Darkmode with a custom Notification.