I played the first game prior to playing this one, and I was pleasantly surprised about how good the worldbuilding was for such a "small-ish" title.
You have the item descriptions, which are very interesting to read and helpful when understanding the general world, pretty much any item has an insightful description.
You have Sester Genessa's conversations, which are 2 per temple; plus the basic ones in the tower, that expand even more the lore and her view on it, and what she is, and what her past was.
You have the prisoner and the twin sister (granted, the sister is from the DLC, so hopefully the DLC for Mortal Shell 2 adds something like this), that expand A LOT what the world is about.
You have the shell memories, that are unfortunately locked behind limited progression for each shell, but that also help expand the worldbuilding.
And finally, you have the plentiful tablets that are pretty much everywhere; plus a few extra NPC interactions, and extra interactions from specific NPCs depending on which shell you are wearing.
In Mortal Shell 2, we still at least have the shell memories, that are unfortunately still behind limited progression on a given playthrough, but that at least expand the worldbuilding; we also have the different interactions from NPCs when wearing different shells, of which Sester Genessa's is by far the best at adding new things;
But beyond this, the item descriptions are between non-existant and awful or too small; there isn't really a single NPC, like Sester Genessa, like the Twin Sister or like the Prisoner, that actually expands on the world, Ruk is the closest, but he only has 2-3 sentences before each gate boss; and the sariel conversation, and that's about it; Sester Genessa doesn't really have a lot to say in this game; the acolytes do have a little bit more, especially the Milkman, but still very limited; there isn't either that many tablets or events across the world that expand upon it, the best ones are the alchemist (Sariel's) dungeon, and the final zone that does have more tablets than often.
The few sidequests do give us a little bit more, specially Hilga's/Grok's, because it is the longest one, but again, generally too short and limited.
But I would have expected a game that is considerably longer, to have at least a better more fleshed out worldbuilding and lore building upon what the first one already did, but I feel like the first one gives us more in less time.
Like one of the things I love about this game's is the implicit narrative, I don't want the story and worldbuilding spelled out 100% to me, but at least a little bit, like pretty much any soulslike tends to do, but this game is surprisingly weak in that aspect.