Deva Mace, one of the outstanding character's strongest weapons, is hard to get in Baldur's Gate 3. In Act 3, your group possesses great gear, but the hidden Deva Mace stands out.
The weapon is in the Stormshore Tabernacle, but it's hard to gain. Steal from the Stormshore Tabernacle and gain the debuff to find the Deva Mace, which deals 1d6 Bludgeoning + 4d6 Radiant damage.
Disarm pressure-plate traps and slide into the back of the chamber to find four goodies. Characters receive the “Castigated by Divinity” penalty when they steal from these chests.
Remember to fight Devas to get the Deva Mace. Other enemies will not drop the mace. If players are willing to combat these winged celestials, they should be able to locate the rest of Baldur's Gate 3's Act 3 secrets.