My wife’s been playing a bunch of it and honestly best I can tell it’s an Unreal Engine tech demo combined with a easy-to-use game engine for beginners to make mini games in (similar to Roblox’s various games) with integrated hosting, release, discovery, authentication and payment processing.

Which is kinda confusing given Epic also has Core which is also an Unreal Engine tech demo combined with easy-to-use game engine with integrated hosting, release, discovery, authentication and payment processing

Oh and Fortnite has its official Battle Royale mode that’s largely a copy of PUBG