Hello Pota2367,
Thanks for using Apple Support Communities, it's great to have you here.
We would recommend checking out this article which goes over how you can change the way your notifications are displayed: Customize your Mail notifications on your iPhone or iPad - Apple Support. From that article, you'll see the following:
Change your Mail notifications
1. In the Settings app, tap Mail.
2. Tap Notifications.
3. Tap Customize Notifications.
4. Tap the email account.
5. Turn on the settings that you want, like Alerts or Badges.
When you turn on Badges, the number of unread emails in your inbox appears above the Mail app on your Home Screen.
The feature you're looking for would likely be "Badges" which shows the amount of unread messages on the Mail icon itself.
Thank you for being a part of the community here. We hope this information helps!
Best wishes.