Modular Sinatra Refactor vs Code Complexity

1-original-impementation.rb

class App < Sinatra::Base
  get '/users' do
    User.all.to_json
  end
  
  post '/users' do
    User.create!(params)
    204
  end
  
  get '/users/:id' do |id|
    User.find(id).to_json
  end
  
  # etc
end

2-intermediate-implementation.rb

# the App looks really nice, but now this is getting a slightly higher Complexity score
module UserRoutes
  def self.registered(app)
    app.get '/users' do
      User.all.to_json
    end
  
    app.post '/users' do
      User.create!(params)
      204
    end
  
    app.get '/users/:id' do |id|
      User.find(id).to_json
    end
  
    # etc
  end
end

class App < Sinatra::Base
  register UserRoutes
end

3-desired-implementation.rb

# combining registered + namespace + routing is instantly complex
module UserRoutes
  def self.registered(app)
    app.namespace '/users' do
      get do
        User.all.to_json
      end
    
      post do
        User.create!(params)
        204
      end
    
      get '/:id' do |id|
        User.find(id).to_json
      end
  
      # etc
    end
  end
end

class App < Sinatra::Base
  register UserRoutes
end

I would like to move from the original, a file which has become very long, to the desired implementation, but Code Climate and Rubocop consider the complexity of the third implementation to be much greater than the original.

What suggestions can be made to both modularize and maintain complexity?