No there's no dark mode theme, just the default theme. It would be nice if theme developers would make dark mode themes that actually worked with dark mode. Right now if you choose a "dark mode theme" (is what Samsung/Theme Store has it categorized as but those themes don't actually theme anything), it only changes the wallpaper and icons. It'd be nice if Samsung would make other colors of the default theme. I'm not a fan of the blue/green colors they are now. I'd prefer pink or an option to choose pink.
Just came upon this thread while trying to figure out how to get the Samsung store app to have a dark theme without needing to turn on dark mode for the rest of my phone...I don't want to have to get rid of the colours for my UI via the phone theme I'm using. Hope there's an update to add a dark theme/setting to the app soon.
