Hi nest18,
Thanks for using Apple Support Communities. It sounds like when you're searching within the Mail application on your Mac, the search results are taking a while to load up. Let's see how we can help.
To confirm, are the results still loading for you when searching, even though it takes longer than expected? Is this only happening when searching within the Mail app, or does it happen when searching in other apps and Spotlight in general, too?
We reviewed your comment on that other thread you shared with us. It looks like you previously restarted your Mac and Mail app, started up in safe mode, and deleted index. To confirm, do you mean you tried rebuilding the mailbox in Mail following these steps: Rebuild mailboxes in Mail on Mac. If not, give that a go for us, too.
When you started up in safe mode, did the behavior continue or resolve? From there, did you follow the additional steps listed in this article: How to use safe mode on your Mac, under 'If the issue continues in safe mode' or 'If the issue doesn't continue in safe mode'?
We look forward to hearing back from you with an update, so we can continue helping out here in the Communities.
Best regards!