I use icloud and this does not match my experience ... apple mail search has been insufficient on ios and macos for 15 years or more at this point ...

IMAP is a horrifically insufficient protocol. Literally every mail provider just implements their own custom JSON protocol to use with their own proprietary apps. Fastmail created JMAP which was meant to be an open source standard but so far only Fastmail uses it so it's just another provider specific protocol and client.