You gotta select full text search on the server. And sometimes it still doesn't work so I'll SSH to my server and just run grep on the mail folder.
Thunderbird use to be awesome, but it's just gradually gotten worse and worse. It's sad because there are literally no other good e-mail clients in the open source world. Evolution is .. okay, not great by any means. I only use it if I'm at a job where I need to connect something to GSuite or Outlook.