Since Mail search stopped working after updating to macOS 27.0 (build 26A434), the update may be related, although the timing alone does not establish the cause.
Apple explains that Spotlight indexing takes place after a software update and can take hours or even days.
During indexing, you may see a progress indicator in Spotlight or a notification from Mail, but the absence of an indicator does not, by itself, establish whether indexing is running. Apple's Spotlight indexing and search troubleshooting guide explains the process and provides steps for rebuilding the index.
Since you have already disabled and re-enabled Mail in Spotlight settings, restarted your Mac, and waited several hours, I would not keep repeating those steps.
The next step is to check System Settings >> General >> Software Update for a newer compatible update.
Apple's instructions for updating macOS explain how to check.
You can also review the official macOS 27 Golden Gate release notes for relevant fixes, although Apple has not confirmed in those notes that this specific Mail search problem is a known bug.
If no relevant fix is available and the problem persists, report it through the Product Feedback - and make it known to Apple regarding this ongoing issue.
Include your Mac model, macOS version and build number, when the problem began, and the troubleshooting steps you've already tried.
Waiting for a future update is an option, but there is no guarantee that an update will resolve the problem.
Given the steps you've already completed, I would report the issue rather than continue repeating them.
