Remove check for enabled feature flag on milestone notes builder

app/services/resource_events/synthetic_milestone_notes_builder_service.rb

@@ -10,8 +10,6 @@ module ResourceEvents
     private
 
     def synthetic_notes
-      return [] unless tracking_enabled?
-
       milestone_change_events.map do |event|
         MilestoneNote.from_event(event, resource: resource, resource_parent: resource_parent)
       end
@@ -23,9 +21,5 @@ module ResourceEvents
       events = resource.resource_milestone_events.includes(user: :status) # rubocop: disable CodeReuse/ActiveRecord
       since_fetch_at(events)
     end
-
-    def tracking_enabled?
-      ::Feature.enabled?(:track_resource_milestone_change_events, resource.project)
-    end
   end
 end

changelogs/unreleased/212985-remove-ff-check-for-synthetic-milestone-notes-creation.yml

+---
+title: Fix missing synthetic milestone change notes for disabled milestone change event tracking feature flag
+merge_request: 28440
+author:
+type: fixed

spec/services/resource_events/synthetic_milestone_notes_builder_service_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ResourceEvents::SyntheticMilestoneNotesBuilderService do
+  describe '#execute' do
+    let_it_be(:user) { create(:user) }
+    let_it_be(:issue) { create(:issue, author: user) }
+
+    before do
+      create_list(:resource_milestone_event, 3, issue: issue)
+
+      stub_feature_flags(track_resource_milestone_change_events: false)
+    end
+
+    context 'when resource milestone events are disabled' do
+      # https://gitlab.com/gitlab-org/gitlab/-/issues/212985
+      it 'still builds notes for existing resource milestone events' do
+        notes = described_class.new(issue, user).execute
+
+        expect(notes.size).to eq(3)
+      end
+    end
+  end
+end