I don't get it.
Just don't use the Gmail interface. Use your own mail reader.
Don't conflate "Gmail the UI" with "Gmail the mail provider".
Having said this - I never used Gmail for anything serious - I had my own domain + mail etc since before Gmail existed, and the reason was I got tired of "free" tools making my life miserable.
> Sure, I could switch to a different mail client and never see any of these language model features, but my experience these past months has left such a bad taste that all I’m looking for now is a clean break.