Default save_description_version_flag to on

app/models/concerns/versioned_description.rb

@@ -16,7 +16,7 @@ module VersionedDescription
   def save_description_version
     self.saved_description_version = nil
 
-    return unless Feature.enabled?(:save_description_versions, issuing_parent)
+    return unless Feature.enabled?(:save_description_versions, issuing_parent, default_enabled: true)
     return unless saved_change_to_description?
 
     unless description_versions.exists?

ee/changelogs/unreleased/issue_36702.yml

+---
+title: View description changes history of issues, epics and merge requests
+merge_request: 27445
+author:
+type: added