Allo there, With armour 2.0 being added with Shadowkeep, armour mods don't sit in your inventory. They sit in their own area inside your armour. They are also elemental. For instance you now get arc, solar and void armour pieces. Some mods that drop have to match that element. So if you're wearing arc gloved and see a solar mod drop then you won't be able to see or equip it unless you inspect a solar set of arms.