For your old emails, use a more private app. iOS Mail is good enough although if you need push for Gmail support, Email by Edison is good as it gives you a single button to press to opt out of Edison Trends.
Their privacy label, in the App Store, is one of the better ones among email clients.
I’m using Proton Mail as my main email. They have an option for forwarding emails from Gmail/Outlook to Proton. I just haven’t done it yet because I almost never use Outlook