Mail Icon doesn’t show count

Hello Zeus023,

Thanks for reaching out to Apple Support Communities. We see you have some questions about your Mail application, and seeing the badge for how many are unread. You're definitely in the right spot for how this should be showing. We'd recommend updating your device, to see if that helps: Update your iPhone or iPad

Update your iPhone or iPad wirelessly

1) Back up your device using iCloud or your computer.

2) Plug your device into power and connect to the internet with Wi-Fi

3) Go to Settings > General, then tap Software Update.

4) If you see more than one software update option available, choose the one that you want to install.

5) Tap Install Now. If you see Download and Install instead, tap it to download the update, enter your passcode, then tap Install Now. If you don't know your passcode, learn what to do.

If that doesn't help, try removing the Mail application from your phone, and install it again. This can sometimes help with badge and notification issues, like you're seeing: Delete built-in Apple apps from the Home Screen on your iOS 14 or later or iPadOS device or Apple Watch

Delete a built-in app from your device

1) On your iOS or iPadOS device, touch and hold the app.

2) Tap Remove App from the shortcut menu.

3) Tap Delete App from the submenu.

Regards.