In principle, since 2017, Google's terms explicitly say they do not scan emails for ad targeting. https://www.theverge.com/2017/6/23/15862492/google-gmail-advertising-targeting-privacy-cloud-business But they do have a long list of 3rd parties who they vet (and then don't police) who have access to read emails https://mashable.com/article/google-reading-your-emails-response 

Google say they can scan emails for "security purposes". 

So, screw Google every which way. Much easier to delete the whole empire from your digital life than play their game of whackamole trying to find the right combination of settings to be shielded from their invasions of privacy. And if there is such a combination, you can bet they will move the goalposts to make sure they still have a way in.