Coding Suggestion

You shall use document.adoptedStyleSheets to avoid the TTP issue for the style adding.

Change from

var css = document.createElement("style");
css.innerText=".ytp-fullerscreen-edu-button { display: none !important; }";
document.head.appendChild(css);

to

let css = new CSSStyleSheet();
css.insertRule(".ytp-fullerscreen-edu-button { display: none !important; }");
document.adoptedStyleSheets.push(css);