Here is a 5-minute Fortnite video showing gameplay on Android
Despite the fact that Fortnite will be exclusively available on the Samsung Galaxy Note 9 for a number of months, that doesn't mean it's not compatible with other Android smartphones. It's just that Epic Games seems to have partnered with Samsung to make the game available on the Note 9 only.
However, the folks over at XDA Developers managed to download the game's installer APK and load it up on a Samsung Galaxy S9+ after bypassing the Fortnite's authentication requirements. They've also been kind enough to record a 5-minute gameplay session to show us how well Fortnite runs on one of Samsung's flagships.
What you see in the video was run at “Epic” graphics quality, but some additional tweaking in the Samsung Game Tuner was made as well to further increase the resolution and performance. Suffice to say, it looks like Fortnite looks and runs flawlessly on the Galaxy S9+, but for those with not so powerful devices, lower graphics settings should probably be used for a smooth gameplay experience.
source: XDA Developers