In don't play DND so not familiar with the Lore. But given the understanding Shar is evil...does playing her as a light Cleric really break that immersion? Doesn't seem like much of a stretch that A Cleric with an Evil God would want to be caster heavy and blow up things with Fireballs.
It's not just a matter of beaning evil. Shar is a goddess of darkness, secrets and sneakiness. And the twin sister polar opposite of Selune goddess of the moon. Shar is an eclipse.
And BG3 is full of imagery associating Shar with darkness. You don't need to be a D&D lore expert for it to be obvious that a light cleric of Shar makes no narrative sense.
It's a case of yes, the game won't stop you doing this, but don't expect the story to still make sense.
Do you care about the story, or do you just want to "beat the game"?
