App or browser?
A native app gives faster load times, biometric login, push notifications and offline caching of the interface. A browser session gives instant access with nothing to install, the full game catalogue rather than a curated subset, and automatic updates.
Most modern casino sites are progressive web apps: you add them to the home screen and get near-app behaviour without an install. For most players that is the best of both, and it avoids app-store availability problems entirely.