How Do I get Mail stop duplicating with new Gmail App?

Hi x25sjhd,

Thanks for visiting Apple Support Communities.

It sounds like you don't want to receive notifications from both the Gmail app and the iOS Mail app, but you don't want to remove your email account from the Mail app. In this case, you can turn off notifications from one of these apps in Settings > Notifications.

Use Notifications on your iPhone, iPad, and iPod touch - Apple Support

Change Notifications settings

Some apps like email or social media apps send frequent notifications, which might affect battery life. If you have Show on Lock Screen turned on for notifications, this also might affect battery life.

To turn off or change notifications, go to Settings > Notifications and select the app. You can also sort your alerts by most recent, order them manually, or group them based on the app.

Best Regards.

Gmail uses IMAP, which syncs all mail "clients". If you had 10 iPhones, each with the gmail account, or a combination of phones and computers, they would all have identical gmail messages. The easiest way to deal with it is to go to Settings/Mail,Contacts,Calendars, tap on the gmail account and turn off the Mail switch. This will remove the gmail inbox and folders from the Mail app.