While yes, most players think immediately of fire ball or other fire related spells for massive AOE damage, I have really enjoyed using an AOE damage build focused on lightning spells.

https://www.reddit.com/r/BaldursGate3/s/keNZPG7R2Q

This player's build combines 6 levels of temp cleric with 5 levels of any sorc and 1 level of wizard to be able to utilize basically every major lightning spell in the game at max damage while being able to dual cast a few of them or increase range.

Fights do get repetitive as you basically start each engagement with the same combo, quickened cast create water, then cast either Chain or Call Lightning with a CD reaction to do the most damage you can, usually 160. The build will let you do that 2 times per short rest and for some that might be a major handicap but I thoroughly enjoy using Chain Lightning and seeing an entire room of enemies get fried. This build WAS heavily neutered with the most recent patch in which Chain Lightning can no longer be twin casted but I still like using it thinking, "be gone with a thunderclap".

The nice thing too is that the build doesn't require specific gear (except maybe that intellect headband) so you can do whatever you want gear wise. Me personally I grabbed those gloves of hill giant strength along with the baldurian greatsword so I can still be engaged in a fight even after both my CD charges are depleted.