NameError When Loading SAML Authentication Plug-in in Redmine 5.0.2

We are deploying saml authentication plug-in in Redmine (5.0.2) for Docker.

The bundle install, bundle execrake has been completed and the deployment itself appears to be successful, but placing the configuration file in /usr/src/redmine/config/initializers results in the following error:

rake aborted!
NameError: uninitialized constant RedmineOmniauthSaml

The configuration file contains the following:

RedmineOmniauthSaml::Base.configure do | config |
  config.saml={
...

I wonder if you are reading the class well, but I wonder if the description method has changed since the Redmine 5 series was introduced.

The environment is Redmine 5.0.2, Ruby 3.1.2-p20, Rails 6.1.6.
Also, I tried Redmine's 4 series using the same plug-in and configuration file, but Redmine itself started without any problems.

I don't really understand ruby, rails, etc., so I would appreciate it if you could give me a hint.