In an effort to organize its mess of Minecraft-branded games, Mojang is consolidating Minecraft Dungeons and Minecraft: Java Edition under a unified launcher. The original Dungeons launcher no longer works, and to play the game, fans need to log in to Minecraft.net and download the Unified Launcher. You could also fire up a copy of Java Edition, which will download the Unified Launcher automatically.
The Unified Launcher isn’t exactly “new,” but this is the first time that Minecraft fans are forced to use it. Updating to the new Unified Launcher won’t affect your save files on Dungeons or Minecraft: Java Edition, although you may need to log in to your Mojang or Microsoft after making the update. Also, while the Unified Launcher brings both games together, you still need to
This change only affects people who purchased Dungeons through Minecraft.net. If you play Dungeons on the Xbox app through Game Pass or a Microsoft Store purchase, then you’re stuck with the Xbox app. You need to purchase both games through Minecraft.net if you want to start them from the Unified Launcher.
It’s also worth mentioning that Minecraft: Windows 10 Edition (formerly Bedrock Edition) does not use the Unified Launcher. If you don’t own a copy of Java Edition, then you need to log in to Minecraft.net and download the Unified Launcher!
Source: Mojang via Windows Central
