Umbral Engrams can be decoded in the Umbral Decoder in the H.E.L.M, Destiny 2's new area for coordinating Guardians efforts during Season of the Chosen. You can also change the Umbral Engrams, which is what makes them so attractive to players.

Who opens Umbral Engrams?

Umbral Engrams drop at your current power level, but they aren't turned in at the Cryptarch or Eververse to crack them open. Instead, you'll need a tool called the Umbral Decoder.

What quest unlocks Umbral Engrams?

To start receiving Umbral Engrams, you must progress through Season of Arrivals' first quest. The mission sends you to The Drifter, who will ask you to set up two new machines in his Tower area. One will decrypt Umbral Engrams and the other will allow you to customize them.