Rails : bootstrapの導入でSyntaxエラーが出る

□ 何かの書き方が問題だとは思うのですが。
https://qiita.com/NaokiIshimura/items/c8db09daefff5c11dadf
この記事に従って、進めました。以前は行けたのですが、Railsのverを6.0に上げたせいかなと思ったりしていますが、原因がわからず。

よろしくお願いします！

js
1// This file is automatically compiled by Webpack, along with any other files
2// present in this directory. You're encouraged to place your actual application logic in
3// a relevant structure within app/javascript and only use these pack files to reference
4// that code so it'll be compiled.
5
6
7require("@rails/ujs").start()
8require("turbolinks").start()
9require("@rails/activestorage").start()
10require("channels")
11
12
13// Uncomment to copy all static images under ../images to the output folder and reference
14// them with the image_pack_tag helper in views (e.g <%= image_pack_tag 'rails.png' %>)
15// or the `imagePath` JavaScript helper below.
16//
17
18//= require jquery3
19//= require popper
20//= require bootstrap-sprockets
21
22// const images = require.context('../images', true)
23// const imagePath = (name) => images(name, true)
24

scss
1
2 //@import "bootstrap";
3 //@import "custom";
4/*
5 * This is a manifest file that'll be compiled into application.css, which will include all the files
6 * listed below.
7 *
8 * Any CSS and SCSS file within this directory, lib/assets/stylesheets, or any plugin's
9 * vendor/assets/stylesheets directory can be referenced here using a relative path.
10 *
11 * You're free to add application-wide styles to this file and they'll appear at the bottom of the
12 * compiled file so the styles you add here take precedence over styles defined in any other CSS/SCSS
13 * files in this directory. Styles in this file should be added after the last require_* statement.
14 * It is generally better to create a new file per style scope.
15 *
16 *= require_tree .
17 *= require_self
18 */
19
20