I've read 'Desolate Era' a couple times now, and the arc structure in the index can feel a bit overwhelming at first. The main ones, going from memory, are the Swallow Mountain Arc, which introduces the setting and Ji Ning's early cultivation struggles. Then it moves into the Stillwater City Arc, where he joins a sect and things get way more complex with different factions. After that, the Grand Xia Dynasty Arc is massive, covering the Celestial Realm Tournament and the war against the Seamless Gate—that's where the scale really explodes.
Later on you get the Three Realms Arc, which is basically the climax of the entire mortal world storyline, ending with that universe-shattering final battle. Post-Three Realms, it jumps into the much broader Chaosverse arcs, like the Ningverse and the Sithe invasion, but honestly those start to blur together for me. The index lists them all, but the real shift happens after the Three Realms; the pacing and stakes change completely. I sometimes think the story has two distinct halves, with the first one being more tightly focused.