Getting Started (Rails) for version 8 and upcoming use the wrong gem version:

gem 'mongoid', '~> 7.0.5'

The Mongoid 8 docs should use gem 'mongoid', '~> 8.0' and upcoming should use a github link to the branch gem 'mongoid', github: 'mongodb/mongoid', branch: 'master'.

Although our Getting Started guide explicitly installs Rails 6.0, the latest version of Rails is 7.0. (This should be updated too.) Rails 7 requires Mongoid 7.3 or later. Thus if you try to follow the guide using the latest version of Rails, you will end up with a broken project.

Similarly the Installation instructions for 8.0 and upcoming provide installation instructions for Mongoid 7.3.0:

gem 'mongoid', '~> 7.3.0'