use union all

app/controllers/templates_dashboard_controller.rb

@@ -57,7 +57,7 @@ class TemplatesDashboardController < ApplicationController
         rel = Template.where(
           Template.arel_table[:id].in(
             rel.where(folder_id: current_account.default_template_folder.id).select(:id).arel
-               .union(shared_template_ids.arel)
+               .union(:all, shared_template_ids.arel)
           )
         )
       else

lib/abilities/template_conditions.rb

@@ -13,7 +13,7 @@ module Abilities
         TemplateSharing.where({ ability:, account_id: [user.account_id, TemplateSharing::ALL_ID] }.compact)
                        .select(:template_id)
 
-      Template.where(Template.arel_table[:id].in(templates.select(:id).arel.union(shared_ids.arel)))
+      Template.where(Template.arel_table[:id].in(templates.select(:id).arel.union(:all, shared_ids.arel)))
     end
 
     def entity(template, user:, ability: nil)