iPhone Screenshots
Description
This is the app I wish I had when I started using a mac.
It allows you to pick custom wallpapers based on light and dark mode.
Once you launch it, it runs in the background, you can see the preferences from the menu icon. Pick the wallpapers you want for light and dark mode, and then enable launch on login. It will automatically change your wallpaper when you switch the appearance.
Once that is done, you can forget about it.