As someone who has not played Fortnite, I have a question. Can I as an independent developer create mods or addons equal to what Epic sells using their in game

As someone who has not played Fortnite, I have a question. Can I as an independent developer create mods or addons equal to what Epic sells using their in game currency and have my mods, skins, etc work in the game? If not, then are they not acting even more egregiously than Apple since Epic has now a "Monopoly" on the Fortnite platform and refuses to allow others to monetize it?