There's plenty of things to like about iOS 11, but auto-playing videos isn't one of them. If you'd prefer to do away with sentient clips while browsing the App Store, Apple does provide a means to disable this functionality.
As is the case with most bundled Apple applications, you'll have to head into Settings to turn this feature on and off. Once it's open, locate "iTunes & App Store" and tap it. Towards the bottom of this section, you'll find an option called "Video Autoplay".
One guess as to what this does.
It's not a simple toggle, however. If you tap this option, you'll be given three choices: On, Wi-Fi Only and Off. If you don't mind the videos and just want to save mobile data, then you can compromise with the middle choice.
Otherwise, just get rid of them entirely.
How To Turn Off App Store Autoplay Videos In iOS 11 [Addictive Tips]