To change your TMDB list's cover to your desired backdrop, open the DevTools Console on your lists page and run this code.

TMDB Any Backdrop as List Cover.js

fetch("https://www.themoviedb.org/list/8283452", { // Replace with your TMDB list ID
    method: "PUT",
    credentials: "include",
    headers: {
        Accept: "application/json, text/javascript, */*; q=0.01",
        "Content-Type": "application/x-www-form-urlencoded; charset=UTF-8",
    },
    body:
        "data=" +
        encodeURIComponent(
            JSON.stringify({
                backdrop_path: "/900tHlUYUkp7Ol04XFSoAaEIXcT.jpg", // Replace with your desired backdrop image path (from TMDB)
            })
        ),
})