Arcane Acuity is a status effect in Baldurs Gate 3 that increases the affected entitys spell Attack Rolls and Spell Difficulty Class by +1 per turn remaining. The condition is capped at 7 stacks for a maximum of +7 Attack and Spell DC). It is a positive status effect that can be acquired through various items such as the Helmet of Arcane Acuity, Hat of Fire Acuity, Hat of Storm Scions Power, Gloves of Battlemages Power, and Elixir of Battlemages Power). The effect can be removed by spending turns in combat, which naturally diminishes it at a rate of one stack per turn).

According to a Reddit post, Arcane Acuity increases spell effectiveness and only spells. It increases attack rolls and spell DC per turn of it, which is more important because spells dont use a lot of attack rolls but a lot of them have save DC. The post also mentions that one gains one spell DC per two scores of their spellcasting abilities (Int, Wis, Cha). The post suggests that Arcane Acuity is more worthwhile to use on a pure spell caster that will bring their main stat up to 18 at level 4 and later 20 at level 8. They also need to have a high enough level in the caster class they are at to ensure they get good spells and access to feats.

In summary, Arcane Acuity is a status effect in Baldurs Gate 3 that increases spell Attack Rolls and Spell Difficulty Class by +1 per turn remaining. It can be acquired through various items and can be removed by spending turns in combat. It is more useful for pure spell casters who have high spellcasting abilities and levels in the caster class.