Well, I’m sorry about it… I found the answer by searching differently in the Ash repo.

So I am sharing a summary in case someone else faces the same concern:

On the relationships you can do the following

relationships do
     belongs_to :tag, MyApp.Organizations.Tag do
      allow_nil? false
      #This description is mapped directly to the GraphQL Fields
      description "Tag assigned to the channel" 
    end
  end

On the attributes you can do the following

 attributes do
    uuid_primary_key :id do
      #This description is mapped directly to the GraphQL Fields
      description "Primary ID"
    end
  end

The one that took me the most to figure out hehe

calculations do
    calculate :channel_id_test, :uuid do
      #This description is mapped directly to the GraphQL Fields
      description "Channel ID where the tag is assigned to"

      calculation fn record, %{api: api} ->
        api.load!(record, :channel).id
      end
    end
  end