One UI Core has only the basic applications required for everyday use of your device. It won't have certain features when compared to One UI. Because it's the stripped-down version of One UI.
In One UI, Galaxy devices will have many features available on it. You can access any samsung apps like Good Lock modules, Secure Folder, Game Launcher and so on. This interface is only for midrange and flagship smartphones.
One UI Core is specifically designed by Samsung for their budget devices. Since they are limited in specs in comparison with flagships.
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