https://www.pcgamer.com/doom-eternal-will-have-have-singleplayer-dlc/

Speaking to Polygon at QuakeCon 2018, game director Marty Stratton confirmed that post-launch, there will be singleplayer DLC for Doom Eternal. "Absolutely," he said when asked about the possibility.

Doom didn't have any singleplayer DLC after its 2016 launch, and Stratton told Polygon that id Software is "already planning that."