You can copy, paste, open the context menu freely.
// ==UserScript==
// @name Copy, Paste and Contextmenu Disabler Disabler
// @name:ja コピー、ペースト、コンテキストメニューの無効化を無効化する
// @namespace http://tampermonkey.net/
// @version 0.3
// @description You can copy, paste, open the context menu freely.
// @description:ja コピペやコンテキストメニューくらい自由に使わせてよ
// @author Jakarta Read-only Brothers
// @include https://*
// @include http://*
// @grant none
// @run-at document-start
// ==/UserScript==
document.addEventListener("copy", (event) => { event.stopImmediatePropagation(); }, true);
document.addEventListener("paste", (event) => { event.stopImmediatePropagation(); }, true);
document.addEventListener("contextmenu", (event) => { event.stopImmediatePropagation(); }, true);