Desmos Duplicate Expression Hotkey. Now bundled into the extension https://github.com/DesModder/DesModder

DesmosDuplicateExpressionHotkey.user.js

// ==UserScript==
// @name        Desmos Duplicate Expression Hotkey
// @namespace   http://github.com/jared-hughes
// @version     0.1
// @author      fireflame241
// @description Binds Ctrl+Q to duplicate the selected expression
// @grant       none
// @match       https://*.desmos.com/calculator*
// ==/UserScript==

/*jshint esversion: 6 */

'use strict';

const waitInterval = setInterval(() => {
    const el = document.querySelector('.dcg-exppanel-outer')
    const Calc = window.Calc
    if (Calc && el) {
        clearInterval(waitInterval)
        el.addEventListener('keydown', e => {
            if (e.code === 'KeyQ' && e.ctrlKey) {
                Calc.controller.dispatch({
                    type: 'duplicate-expression',
                    id: Calc.selectedExpressionId,
                })
            }
        })
    }
}, 50)