The iPhone uses badges to indicate that a new message, email, push notification, or voicemail is waiting.
https://discussions.apple.com/thread/250735184#:~:text=The i...

When using Thunderbird or Apple Mail, there is always a 'New Mail' badge against the relevant email account.
https://www.elevenforum.com/t/unread-mail-badge-on-outlook-e...

You can also set the display time and transparency of system tray notifications (this applies only on systems that support system tray notifications)
https://docplayer.net/141929751-Eset-endpoint-antivirus.html

The admin has the choice of how long the badge is displayed. It remains on display unless it is turned off by an admin for other members in...
https://blog.groupleads.net/facebook-group-admin-tools/