Apple's apps tend to be the fastest to adopt the latest app standards, but the Apple Store apps for iOS haven't been adapted to dark mode. Recently, the app has finally been updated to accommodate the dark color mode.
The Apple Store app is currently updated to version 5.8.
Dark mode is seamlessly embedded in the app, allowing you to browse, buy and explore in this new mode
Multiple problem fixes and functional enhancements
When you turn on the dark mode switch in the Control Center, the Apple Store's interface follows the switch to dark mode with a black background.
In fact, since Apple implemented iOS 13, many third-party apps have not been adapted in the first place, except at the system level and some of its own apps.