Remove next line from config/application.rb
require "active_storage/engine"
Remove next line from environments config/environments/*.rb
config.active_storage.service = :local
Remove next line from app/assets/javascripts/application.js
//= require activestorage
ActiveStorage rails routes will vanish
In case there is statement require 'rails/all' in application.rb then you can use solution provided below where you need to require dependency by dependency and to omit active_storage.