Hi!
Welcome to the Microsoft Q&A forum.
Based from your screenshot, this is a hardcoded warning by design whenever the Windows Search service is disabled. As of now, there is no supported registry key, group policy, or hidden setting that removes the banner without re-enabling indexing.
I suggest that you submit a feedback via Feedback hub. Press Win + F (This keyboard shortcut opens Feedback Hub). From here you can search if there are any logs similar to your request. If there are no requests you can proceed providing a feedback.