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.
‘Minecraft Dungeons’ and ‘Minecraft: Java Edition’ Now Share a Unified Launcher