GameShare is the multiplayer-sharing feature that lets Pokémon Pokopia visitors play without owning the game.
Nintendo describes GameShare as a way for players to invite visitors who do not have their own copy of Pokopia. The feature is associated with Nintendo hardware sharing and is separate from simply owning the game on another account.
Pokopia also supports multiplayer in other ways, including visits and shared play with friends. That broader multiplayer support can make the feature names easy to mix up, especially because Nintendo uses different sharing systems across its games and consoles.
GameShare does not mean that the game is available on every Nintendo platform. Pokopia remains a Nintendo Switch 2 title, while GameShare concerns how a compatible host can share access during multiplayer play.