overleaf_editor_enhancer.user.js

// ==UserScript==
// @name         Overleaf Editor Enhancer
// @namespace    https://gist.github.com/indirivacua/1b9c878c5b7e3487be7ca5fb384ff286
// @version      0.1
// @description  This script aims to improve productivity and user experience on Overleaf LaTeX editor.
// @author       indirivacua
// @match        https://*.overleaf.com/project/*
// @icon         https://images.ctfassets.net/nrgyaltdicpt/h9dpHuVys19B1sOAWvbP6/5f8d4c6d051f63e4ba450befd56f9189/ologo_square_colour_light_bg.svg
// @grant        none
// @license      MIT
// @updateURL    https://gist.github.com/indirivacua/1b9c878c5b7e3487be7ca5fb384ff286/raw/overleaf_editor_enhancer.user.js
// ==/UserScript==

(function() {
    'use strict';

    setTimeout(function () {
        var toolbar = document.querySelector('div.toolbar-editor');
        var buttonGroup = document.createElement('div');
        buttonGroup.className = "ol-cm-toolbar-button-group";
        var element = document.createElement('img');
        element.src = "data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='1em' height='1em' viewBox='0 0 24 24'%3E%3Cpath fill='%23000' d='M14.7 20.7L11 17l3.7-3.7l1.4 1.45L14.85 16h2.4q.725 0 1.238-.513T19 14.25t-.513-1.237t-1.237-.513H4v-2h13.25q1.575 0 2.663 1.088T21 14.25t-1.088 2.663T17.25 18h-2.4l1.25 1.25zM4 18v-2h5v2zM4 7V5h16v2z'/%3E%3C/svg%3E";
        element.className = "ol-cm-toolbar-button btn";
        element.onclick = function() {
            var editor = document.querySelector('.cm-content');
            editor.classList.toggle("cm-lineWrapping");
        };
        element.title = "Toggle Line Wrap";
        buttonGroup.appendChild(element);
        toolbar.insertBefore(buttonGroup, toolbar.children[1]);

        var button = document.querySelector('button.ol-cm-toolbar-button-math');
        button.addEventListener('click', function() {
            setTimeout(function() {
                var overlay = document.querySelector('div.symbol-palette-overlay.small');
                overlay.parentNode.removeChild(overlay);
            }, 1000);
        });
    }, 3000);
})();

Line 26, add:
element.title="Toggle Line Wrap";