Installation fails on Ubuntu 20.04 LTS distro Redmine 4.0

[gnudiff]

Brand new redmine installation from Ubuntu 20.04LTS apt repository:
Environment:
Redmine version 4.0.6.stable
Ruby version 2.7.0-p0 (2019-12-25) [x86_64-linux-gnu]
Rails version 5.2.3
Environment production
Database adapter PostgreSQL
Mailer queue ActiveJob::QueueAdapters::AsyncAdapter
Mailer delivery smtp
SCM:
Git 2.25.1
Filesystem
Redmine plugins:
no plugin installed

When following the installation instructions, I get the following error when trying to execute migration:

#rake redmine:plugins:migrate RAILS_ENV=production
/usr/share/rubygems-integration/all/gems/activerecord-5.2.3/lib/active_record/type.rb:27: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/usr/share/rubygems-integration/all/gems/activerecord-5.2.3/lib/active_record/type/adapter_specific_registry.rb:9: warning: The called method `add_modifier' is defined here
/usr/share/rubygems-integration/all/gems/activerecord-5.2.3/lib/active_record/associations.rb:1855: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/usr/share/rubygems-integration/all/gems/activerecord-5.2.3/lib/active_record/associations.rb:1368: warning: The called method `has_many' is defined here
/usr/share/rubygems-integration/all/gems/actionpack-5.2.3/lib/action_dispatch/middleware/stack.rb:37: warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
/usr/share/rubygems-integration/all/gems/actionpack-5.2.3/lib/action_dispatch/middleware/static.rb:111: warning: The called method `initialize' is defined here
rake aborted!
NameError: uninitialized constant Rich
/usr/share/redmine/lib/plugins/redmine_ckeditor/lib/redmine_ckeditor.rb:136:in `apply_patch'
/usr/share/redmine/lib/plugins/redmine_ckeditor/init.rb:5:in `block (2 levels) in <top (required)>'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:426:in `instance_exec'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:426:in `block in make_lambda'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:198:in `block (2 levels) in halting'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:606:in `block (2 levels) in default_terminator'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:605:in `catch'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:605:in `block in default_terminator'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:199:in `block in halting'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:513:in `block in invoke_before'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:513:in `each'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:513:in `invoke_before'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/callbacks.rb:131:in `run_callbacks'
/usr/share/rubygems-integration/all/gems/activesupport-5.2.3/lib/active_support/reloader.rb:89:in `prepare!'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/application/finisher.rb:63:in `block in <module:Finisher>'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `instance_exec'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/initializable.rb:32:in `run'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/initializable.rb:61:in `block in run_initializers'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/initializable.rb:60:in `run_initializers'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/application.rb:361:in `initialize!'
/usr/share/redmine/config/environment.rb:14:in `<top (required)>'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/application.rb:337:in `require'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/application.rb:337:in `require_environment!'
/usr/share/rubygems-integration/all/gems/railties-5.2.3/lib/rails/application.rb:520:in `block in run_tasks_blocks'
/usr/share/rubygems-integration/all/gems/rake-13.0.1/exe/rake:27:in `<top (required)>'
Tasks: TOP => redmine:plugins:migrate => environment
(See full trace by running task with --trace)

Apparently "rich" is not included and is not autoinstalled? I tried to get rich gem by hand, but wasn't able to get v1.5.2 (which is required in ckeditor gemfile), only could get 1.4.8., which fails to rake on the same Ubuntu, noting I have to use different versions of bundler, etc.