Act Three is where the story of Baldur's Gate 3 ends and all major plot points conclude. With the amount of variation that can occur based on your choices, you should know what quests you need to complete before tackling the main storyline.
Things to Miss in Act 3 – Baldur's Gate 3
To make it easier for you, we've created a checklist of all the important things you need to do before finishing the main story.
The checklist described here only contains missions, apart from the main questline which revolves around collecting the Netherstones.
Completing these activities will make the main missions easier and you will gain rewards and new companions if you play your cards right.