Angelbreath is a material that became increasingly important with the release of the Vessel of Hatred DLC in Diablo 4. You will need this to craft some powerful elixirs. These can be especially helpful when challenging tough enemies. Elixirs are consumable items that temporarily boost your damage or resistance in combat. You will need plenty of Angelbreath to keep your supply up.

https://screenrant.com/diablo-4-angelbreath-guide/