Hello Omonroy,
Thank you for using Apple Support Communities!
It is our understanding from your post that when searching emails in the Mail app on your Mac it is taking longer than expected to get results if you get any at all. We recommend testing the issue while your Mac is in safe mode. The following articles have the steps you will need to test the issue in safe mode:
How to use safe mode on your Mac - Apple Support
"Safe mode prevents your Mac from loading certain software as it starts up, including login items, system extensions not required by macOS, and fonts not installed by macOS. It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. And it deletes some system caches, including font caches and the kernel cache, which are automatically created again as needed."
Best Regards.