Cloud9からHerokuへデプロイしたいです

前提・実現したいこと

初学者です。railsを勉強中です。
cloud9からherokuにデプロイできている状態を実現したいです。
ご回答いただけますと幸いです。

web業界のお作法がまだ、あまり土地勘がなく
不足点ございましたら、ご指摘いただけますと幸いです。

※補足※
Railsチュートリアルで第1章をやっており、最後のherokuでデプロイする場所で
詰みました。ネット上にあるものはいろいろ拝見して試しましたが解決できませんでした。

■■な機能を実装中に以下のエラーメッセージが発生しました。

発生している問題・エラーメッセージ

ubuntu:~/environment/hello_app (master) $ git push heroku master
Counting objects: 110, done.
Compressing objects: 100% (92/92), done.
Writing objects: 100% (110/110), 26.81 KiB | 1.17 MiB/s, done.
Total 110 (delta 7), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote: 
remote: -----> Building on the Heroku-20 stack
remote: -----> Determining which buildpack to use for this app
remote:  !     Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote:                         Detected buildpacks: Ruby,Node.js
remote:                         See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote: -----> Installing bundler 1.17.3
remote: -----> Removing BUNDLED WITH version in the Gemfile.lock
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.7.4
remote: -----> Installing dependencies using bundler 1.17.3
remote:        Running: BUNDLE_WITHOUT='development:test' BUNDLE_PATH=vendor/bundle BUNDLE_BIN=vendor/bundle/bin BUNDLE_DEPLOYMENT=1 BUNDLE_GLOBAL_PATH_APPENDS_RUBY_SCOPE=1 bundle install -j4
remote:        The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
remote:        Fetching gem metadata from https://rubygems.org/............
.
.
.
remote:        Fetching webpacker 4.0.7
remote:        Installing sass-rails 5.1.0
remote:        Installing rails 6.0.3
remote:        Installing webpacker 4.0.7
remote:        Bundle complete! 18 Gemfile dependencies, 60 gems now installed.
remote:        Gems in the groups development and test were not installed.
remote:        Bundled gems are installed into `./vendor/bundle`
remote:        Post-install message from sass:
remote:        
remote:        Ruby Sass has reached end-of-life and should no longer be used.
remote:        
remote:        * If you use Sass as a command-line tool, we recommend using Dart Sass, the new
remote:          primary implementation: https://sass-lang.com/install
remote:        
remote:        * If you use Sass as a plug-in for a Ruby web framework, we recommend using the
remote:          sassc gem: https://github.com/sass/sassc-ruby#readme
remote:        
remote:        * For more details, please refer to the Sass blog:
remote:          https://sass-lang.com/blog/posts/7828841
remote:        
remote:        Removing bundler (1.17.3)
remote:        Bundle completed (35.71s)
remote:        Cleaning up the bundler cache.
remote: -----> Installing node-v12.16.2-linux-x64
remote: -----> Installing yarn-v1.22.4
remote: -----> Detecting rake tasks
remote: -----> Preparing app for Rails asset pipeline
remote:        Running: rake assets:precompile
remote:        yarn install v1.22.4
remote:        info No lockfile found.
remote:        [1/4] Resolving packages...
remote:        warning webpack-dev-server > sockjs > uuid@3.4.0: Please upgrade  to version 7 or higher.  Older versions may use Math.random() in certain circumstances, which is known to be problematic.  See https://v8.dev/blog/math-random for details.
remote:        warning webpack-dev-server > url > querystring@0.2.0: The querystring API is considered Legacy. new code should use the URLSearchParams API instead.
remote:        [2/4] Fetching packages...
remote:        info fsevents@2.3.2: The platform "linux" is incompatible with this module.
remote:        info "fsevents@2.3.2" is an optional dependency and failed compatibility check. Excluding it from installation.
remote:        [3/4] Linking dependencies...
remote:        warning " > webpack-dev-server@4.4.0" has unmet peer dependency "webpack@^4.37.0 || ^5.0.0".
remote:        warning "webpack-dev-server > webpack-dev-middleware@5.2.1" has unmet peer dependency "webpack@^4.0.0 || ^5.0.0".
remote:        [4/4] Building fresh packages...
remote:        Done in 6.78s.
remote:        I, [2021-11-02T08:56:42.766727 #1080]  INFO -- : Writing /tmp/build_390456f0/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css
remote:        I, [2021-11-02T08:56:42.767226 #1080]  INFO -- : Writing /tmp/build_390456f0/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css.gz
remote:        Compiling…
remote:        Compilation failed:
remote:        error Command "webpack" not found.
remote:        
remote:        yarn run v1.22.4
remote:        info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.
remote:        
remote: 
remote:  !
remote:  !     Precompiling assets failed.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...
remote: 
remote: !       Push rejected to frozen-sands-92281.
remote: 
To https://git.heroku.com/frozen-sands-92281.git
 ! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/frozen-sands-92281.git'
ubuntu:~/environment/hello_app (master) $

該当のソースコード

#package.jsonの中身です
{
  "name": "hello_app",
  "license": "UNLICENSED",
  "private": true,
  "dependencies": {
    "@rails/actioncable": "^6.0.0",
    "@rails/activestorage": "^6.0.0",
    "@rails/ujs": "^6.0.0",
    "@rails/webpacker": "^5.4.3",
    "turbolinks": "^5.2.0",
    "yarn": "^1.22.17"
  },
  "version": "0.1.0",
  "devDependencies": {
    "webpack-dev-server": "^4.4.0"
  },
  "description": "The best package you will ever find.",
  "main": "index.js",
  "repository": "https://github.com//hello_app.git",
  "author": "Yarn Contributor"
}

試したこと

①yarnからwebpackerを削除　［参照］https://www.somethinggood.work/151
→しかし、下記の通りpackage.jsonの影響でエラーになります。
warning ../../package.json: No license field
[1/2] Removing module webpack...
error This module isn't specified in a package.json file.

②package.jsonでlicense fieldを追記して、再度①を実行　［参照］https://qiita.com/kozakura16/items/ebaf8ea58fc49dcbdd73
→再度、①と同様のエラーが出ます
warning ../../package.json: No license field
[1/2] Removing module webpack...
error This module isn't specified in a package.json file.

③yarnを再インストール［参照］
→やはり、package.jsonが悪さをしてそう&linuxもうまくいってなさそう
ubuntu:~/environment/hello_app (master) $ yarn install --check-files
yarn install v1.22.15
warning ../../package.json: No license field
[1/4] Resolving packages...
[2/4] Fetching packages...
info fsevents@2.3.2: The platform "linux" is incompatible with this module.
info "fsevents@2.3.2" is an optional dependency and failed compatibility check. Excluding it from installation.
info fsevents@1.2.13: The platform "linux" is incompatible with this module.
info "fsevents@1.2.13" is an optional dependency and failed compatibility check. Excluding it from installation.
[3/4] Linking dependencies...
warning " > webpack-dev-server@4.4.0" has unmet peer dependency "webpack@^4.37.0 || ^5.0.0".
warning "webpack-dev-server > webpack-dev-middleware@5.2.1" has unmet peer dependency "webpack@^4.0.0 || ^5.0.0".
[4/4] Building fresh packages...
Done in 5.96s.
※再度、①をやっても同様のエラー発生