Here you go the working version:
// ==UserScript==
// @name Freeship
// @namespace lemons
// @version 1.5
// @description Unlock all Fireship PRO courses/lessons.
// @author lemons
// @match https://fireship.io/*
// @icon https://emojipedia-us.s3.dualstack.us-west-1.amazonaws.com/thumbs/120/apple/325/fire_1f525.png
// @grant none
// @downloadURL https://update.greasyfork.org/scripts/455330/Freeship.user.js
// @updateURL https://update.greasyfork.org/scripts/455330/Freeship.meta.js
// ==/UserScript==
setInterval(async () => {
document.querySelectorAll("[free=\"\"]").forEach(el => el.setAttribute("free", true)) // set all elements with the attribute free set to "" to true
if (document.querySelector("if-access [slot=\"granted\"]")) { // replace HOW TO ENROLL to YOU HAVE ACCESS
document.querySelector("if-access [slot=\"denied\"]").remove()
document.querySelector("if-access [slot=\"granted\"]").setAttribute("slot", "denied")
}
if (document.querySelector("video-player")?.shadowRoot?.querySelector(".vid")?.innerHTML) return; // return if no video player
const vimeoId = Number(atob(document.querySelector("global-data").vimeo)) - Number(document.querySelector("head").getAttribute("data-build")); // get id for vimeo video
const youtubeId = atob(document.querySelector("global-data").youtube); // get id for vimeo video
if (vimeoId) { // if there is an id,
document.querySelector("video-player").setAttribute("free", true) // set free to true
const html = (await fetch(`https://vimeo.com/api/oembed.json?url=https%3A%2F%2Fvimeo.com%2F${vimeoId}&id=${vimeoId}`).then(r=>r.json())).html
document.querySelector("video-player").shadowRoot.querySelector(".vid").innerHTML = html // set video
}
if (youtubeId) { // if there is an id,
document.querySelector("video-player").setAttribute("free", true) // set free to true
document.querySelector("video-player").shadowRoot.querySelector(".vid").innerHTML = `<iframe src="https://youtube.com/embed/${youtubeId}" allow="autoplay; fullscreen; picture-in-picture" allowfullscreen="" title="${location.pathname.split("/")[3]}" width="426" height="240" frameborder="0"></iframe>` // set video
}
}, 100)