There isn't yet a game that involves all the players in one huge level, without shards, but there might be eventually. Current game engines don't support levels with that many players simultaneously. There is an interview with Neal Stephenson and Tim Sweeney on the Metaverse where Sweeney says supporting massive multiplayer is what he plans for Unreal Engine 6: https://www.matthewball.co/all/sweeneystephenson

> So one of the big efforts that we're making for Unreal Engine 6 is improving the networking model, where we both have servers supporting lots of players, but also the ability to seamlessly move players between servers and to enable all the servers in a data center or in multiple data centers, to talk to each other and coordinate a simulation of the scale of millions or in the future, perhaps even a billion concurrent players. That's got to be one of the goals of the technology. Otherwise, many genres of games just can never exist because the technology isn't there to support them. And further, we've seen massively multiplayer online games that have built parts of this kind of server technology. They've done it by imposing enormous costs on every programmer who writes code for the system. As a programmer you would write your code twice, one version for doing the thing locally when the player's on your server and another for negotiating across the network when the player's on another server. Every interaction in the game devolves into this complicated networking protocol every programmer has to make work. And when they have any bugs, you see item duplication bugs and cheating and all kinds of exploits. Our aim is to build a networking model that retains the really simple Verse programming model that we have in Fortnite today using technology that was made practical in the early 2000's by Simon Marlow, Simon Peyton Jones and others called Software Transactional Memory.