To unlock the Poof! trophy in Far Cry New Dawn, you must simply use 3 smoke grenades.
You will need the following items to craft a smoke grenade in Far Cry New Dawn:
Yukka: Plant commonly found in forests.
Black Powder: Looting dead bodies and containers. Also from trading animal skins and fish.
One of each item is required to craft a smoke grenade, so three of each in total to craft the three needed for the Poof! trophy.
To craft a grenade, open the weapon will with L1 and use up or down on the D-Pad until you reach smoke grenades. Select and hold Square to craft.
Once you have three, you can simply throw them. You do not have hit any enemies for it to count.