If you've updated to iOS 14 on your iPhone and would like to set Gmail as the default email client, the following article from Dave Taylor explains how. I just did that on my iPhone X and had to go first to the app store and update my Gmail app. Once updated, the change is then easy to do.
Jim Hamm
https://www.askdavetaylor.com/change-default-email-program-to-gmail-on-my-ios14-iphone/