Destiny 2 Cloud Accretions are a new resource that's unique to Neptune's city of Neomuna. Just like the Fundamental Osmium in the Witch Queen's Throne World, harvesting these nodes is a great way to get some extra reputation with Nimbus, unlocking new activities, gear, and quests.
This resource also plays an important part in the Unfinished Business quest you get after completing the Lightfall campaign, which gives you that new exotic machine gun, Deterministic Chaos. If you're still working through the campaign, then you might want to know how to solve that Headlong mission puzzle (opens in new tab) with the harpies.
Otherwise, here's the best way to find Cloud Accretions in Neomuna, and how to complete the quest step involving them in Unfinished Business.
Where to find Cloud Accretions in Neomuna
Since Cloud Accretions are Neomuna's specific regional resource, you can find them all over the city. However, the best way to get some quickly is to equip a resource finder mod on your ghost. The Perfected Resource Detector mod takes up five energy slots, but it detects Cloud Accretions within a 75-meter radius, highlighting them with a triangular resource symbol, and making it much easier to collect them.
One of the best areas to get Cloud Accretions is the Zephyr Concourse, as you can run around doing the Terminal Overload event at the same time, and quickly grabbing the resources when they come into range. The Unfinished Business quest is a little more fiddly than just collecting Cloud Accretions, though.
Once you have the quest you'll need to defeat Vex to collect Qubits—eight of them to be exact—then find a Cloud Accretion to extract a Data Packet from it. You'll have to repeat this process five times overall, so, Liming Harbor is likely the best location for you to hang out. There are tonnes of Vex to kill here, so you can take their qubits to nearby Cloud Accretions. That said, Zephyr Concourse is still a good option for this when the Terminal Overload event is active, as this often includes a lot of Vex enemies.