The official release date of Doom Eternal has been pushed back until March 2020 according to the games developer ID software.
In a blog post below the developer explains why
Doom Eternal Release Date
Doom Eternal has been delayed until march 2020 to make sure the state of the game is good enough for players, however some other features will be available at launch.
Doom Eternal New Content
Invasion Mode – which will allow players to enter another players game as a playable demon.
The Nintendo switch version will arrive shortly after other platforms.
Doom 64 will be arriving as a pre order bonus for players.