If I understand correctly, a gerund is the noun form of a verb- a verb turned into a noun. “A building is building” the first building is a noun, it is the thing being built. The second is a verb, the act of being built. Google tells me gerunds are supposed to end in -ing, but “reddit is an enshittifying” doesn’t quite sound right, so I used an adjective form. It’s very possible I don’t understand correctly.