Earlier quoted context omitted.
At the very least, I can confirm that ProtonMail and Apple's Mail clients let you search through the message contents of encrypted email. I'm sure there's a performance hit, and admins wouldn't be able to search through the encrypted emails of their Workspace users, but that's a much more reasonable tradeoff.
I'd be interested to know the implementation... Most search-over-encrypted-documents implementations either don't scale well (eg. require the client to do all the indexing and upload the encrypted index), or have reduced privacy (allowing the server to infer which words are in which document).
Or just require the client to do the indexing and the searching, and not upload the index anywhere.