Quests that you can't decline have ruined this game they are "expletive" pointless, make nightshade 20 times even though you don't need any more but the game is so controlling of how you play it BORING or what , creators need to sort their game out.
All chapter-specific quests becomae declinable once you move to the next chapter. Ignore it, and then once you're in the next chapter you can just do the quests you want to do and decline the rest.