Mail 16 search doesn't work
Mail 16, OS 15.1
Mac mini, macOS 15.1
Rebuild your Spotlight index.
Rebuild the Spotlight index on your Mac
Rebuild the Spotlight index on your Mac - Apple Support (CA)
Drag your Macintosh HD into Spotlight and then remove it. Depending on how much you have on your system it could take awhile.
or you could use Terminal
In the Terminal, type sudo mdutil -E / and hit return. You may have to enter your password.