There’s been a lot of discussions regarding Destiny 2’s methods of procuring Exotics, especially new ones added with each season and expansion. While they’re acquired randomly, the only way to farm them is through Legend and Master Lost Sectors. With the game receiving more Exotics over time, getting the one you want with the right roll became a massive time-sink.
Following the release of Lightfall, the difficulty of Lost Sectors increased significantly. Though Bungie has since toned down enemy health, the farming methods were still iffy. The developer will address this in Season 21, aka Season of the Deep, with Exotic Armor focusing.
Exotic Engrams from activities like Nightfalls, Lost Sectors and Vex Strike Force on Neomuna (which will award Exotics on a knockout basis) won’t decrypt. You can take them to Master Rahool and use Advanced Decryption to obtain an Exotic from previous expansion eras like Shadowkeep, Beyond Light, The Witch Queen, and so on. It costs one Exotic Engram, one Ascendant Shard and 30,000 Glimmer.
For a specific Exotic, Precision Decryption is an option, though it requires three Ascendant Shards, one Exotic Engram, one Exotic Cipher and 60,000 Glimmer. You can only hold one Exotic Cipher currently, but the plan is to raise the limit to five.
Of course, you can also decrypt them for free and roll the dice. Furthermore, new Exotics can’t be obtained through Focusing. You must “unlock” them first from Vex Strike Force or Lost Sectors. Bungie is “looking to move acquiring new armor to a more accessible location” in the future, so stay tuned.