Microsoft has partnered with Epic Games to make Fortnite available on supported browser-enabled devices for free with Xbox Cloud Gaming in 26 countries.
This means that starting today, you can play Fortnite in cloud-supported markets just by having a Microsoft account and an iOS, iPadOS, Android phone or tablet, or Windows PC with internet access.
Since you don’t need to install the game, all you need to do is go to Xbox.com/play on your web browser and sign-in with your Microsoft Account and start playing Fortnite.