At what boss difficulty does megalomaniac diamond begin to drop?

Every Wikipedia page says it drops at difficulty 4 for the boss but when you go to add the currency to the gate there's only three difficulty levels now?

Not a single Wikipedia page or website has updated their info on this it's all old info from last League... Help?

Now it drops in any simulacrum tier but the higher it is the most chance to get , i think is like 20% in the highest.

Is that how it works now for every boss every item has a chance at any difficulty tier? Because that's really nice to know for farming.