The DLC in all the games are fairly important depending on the DLC/expansion, and there can be a lot of it. DA2 and DAI both integrate well into the story while DAO was kind of built around the idea of side-story mini-adventures so there's a lot more of them.

DAO Primary story DLC: Warden's Keep, Stone Prisoner, Return to Ostagar add side quests to the main game and are solid to play.

DAO Standalone campaigns: Leliana's Song is a prequel focusing on the Leliana party member (you'll meet her pretty early in DAO although she is missable), Darkspawn Chronicles is an alternate history and not needed although fun, Golems of Amgarrak is a short post-story adventure that's not that important, Witch Hunt is a post-game story around Morrigan that's actually pretty important.

Awakening is a full-length expansion and absolutely worth playing, some of the characters you meet here tie into DA2.

DA2: All DLC integrates with the main story and can be played at any time. Legacy is a very important DLC that directly ties into Dragon Age Inquisition.

DAI: All 3 story DLC are fantastic, Jaws of Hakkon, The Descent and Trespasser.
Jaws and Descent are played during the main story as side quests, and Descent has some major lore implications for the world and raises some serious questions about the past and the potential future. Trespasser is a post-game story that directly leads into DA4: Dreadwolf when it comes out.

Also not sure if Gamepass supports this, but you can import your saves forward. For Dragon Age Inquisition you will need to use Dragon Age Keep to recreate your choices to import them into your world state.