migration.rb

class AddFeatureGroupIdToFeatures < ActiveRecord::Migration[6.0]
  def change
    add_refererence :features, :feature_group, foreign_key: true
  end
end

models.rb

class Feature < ApplicationRecord
  has_many :products, through: :product_features
  has_many :product_features
  belongs_to :feature_group 
end

class FeatureGroup < ApplicationRecord
  has_many :features
  has_many :products, through: :features
end

class ProductFeature < ApplicationRecord
  belongs_to :feature
  belongs_to :product
  # default scope should be avoided
end

class Product < ApplicationRecord
  has_many :product_features
  has_many :features, through: :product_features
  has_many :feature_groups, through: :features
end