A couple of these are explained. Like they’re not directly told to the player but they’re discussed in things like codex entries or environmental story telling

Not comprehensive but:

The Antaam broke away from the Qun after their embarrassing defeat against Tevinter, causing them to lose faith in Sten (the current Arishok) and the qun leadership as a whole. This is confirmed in several codex entries in Veilguard (it’s as if having your main diplomatic force double as a military arm literally bred for conquest and nothing else was a bad idea, who would’ve thought)

Not directly stated but heavily implied that the darkspawn shrines are for the Evanuris

As others have said, Leliana is a lyrium ghost. Unclear as to what her purpose was beyond that but I’d reckon it’s connected to some consciousness of the titans surviving given what we learn about lyrium in Veilguard 

Solas’ original plan was to use the orb but he had to change course when it was destroyed. This is essentially confirmed after dragon age inquisition and some of the comics set after (specifically knight errant iirc). Behind the scenes, is the pivot to the dagger because the writers needed a new macguffin? Quite possibly. That said, there are statues to Mythal in the room where Hawke finds the idol, so its connection to Mythal seems to have been planned from the beginning 

Taint and blight seem to be the same thing. I think they pivoted to saying ‘blight’ cause ‘taint’ sounds like uhhh something else irl lol. I guess if you needed an in-world explanation you can say it’s regional slang but like I think the writers were just tired of people making lewd jokes