About the documentation. Would it be worth to update https://guides.solidus.io/customization/customizing-the-backend/#adding-new-menu-items to clarify more about the

SolidusAdmin

. It took me a bit of time to notice that I needed both:

if defined?(SolidusAdmin)
  SolidusAdmin::Engine.routes.draw do
    get '/about', to: 'about#index', as: :about
    get '/about/:id', to: 'about#show', as: :about_show
  end
end

Spree::Core::Engine.routes.draw do
  namespace :admin do
    get '/about', to: 'about#index', as: :about
    get '/about/:id', to: 'about#show', as: :about_show
  end
end