Rails' Webpacker :: Manifest :: MissingEntryError seems to be a beginner. But I was able to solve it immediately.
Rails6, MySQL was built with Docker. ↓ "yay, you are on rails!" ↓ Start writing immediately, change the root directory, write a view, and check with a browser. ↓ Webpacker::Manifest::MissingEntryError
bundle exec rails webpacker:install
Other method https://github.com/rails/webpacker/issues/1730 https://blog.yuhiisk.com/archive/2018/04/24/rails-error-collection.html#Webpacker