The "Mythic Dungeons" row has been renamed to "Dungeons."
Heroic, Mythic 0, and Timewalking dungeon runs now unlock rewards in the Dungeons row. These draw from the same rewards pool as Mythic+, with lower item levels. Timewalking dungeon runs count as Heroic.
New changes in season 3:
Source: https://worldofwarcraft.blizzard.com/en-us/news/24020034/updated-nov-1-dragonflight-guardians-of-the-dream-content-update-notes