Doom 2016 begins with the Slayer locked in a coffin with all his friends long-dead, and Doom Eternal goes into greater detail ...
TL;DR: DOOM: The Dark Ages explores a medieval chapter in the Doom saga, distinct from its predecessors. It avoids a direct tie-in to DOOM (2016) by not ending with the Doomslayer in a coffin ...
There might be room to expand in the medieval setting after Doom: The Dark Ages. Here's what the game director had to say.