The biggest difference between the Cloud and Dark spells in Baldur's Gate 3 is that the Cloud spells can shoot inside and out, and they can shoot both inside and outside, but the Dark spells cannot attack, so it is still not recommended for players to use the Dark spells. In terms of damage and The effect is the same for both.
Difference introduction
The cloud and mist technique can be used to shoot from the inside to the outside, and it can be used from the outside to the inside.
Dark magic means that the inside cannot shoot out, the inside cannot shoot inside, and the outside cannot shoot inside.
cloud magic
This is to create a thick fog on the target during the round, and then make the creatures inside blind.
Creatures cannot attack inside the darkness. Players can block the target's sight after using this spell.
Darkness
This can create a magical black cloud during battle and can also blind the enemy.