https://wccftech.com/luigis-mansion-3-update-1-2-0/

Nintendo has rolled out Luigi’s Mansion 3 Update 1.2.0 for the Nintendo Switch which adds a DLC button to the title menu ahead of the game’s freshly announced upcoming multiplayer DLC packs.

Alongside the new DLC button, the Luigi’s Mansion 3 update fixes various story and general issues that should improve the gameplay experience. For instance, Nintendo writes that the issue that prevented the game from progressing when going down to B2 in the elevator, has been fixed. In addition, Luigi’s Mansion 3 Update 1.2.0 addresses and issue that prevented Luigi from leaving the building in Studio 3 on the Paranormal Productions floor.