Apple Tv shows 1 notification.

You may find notifications in Notification Center. For the TV app, it could be something like “a new episode of show X is now available”. You can turn off notification badges in System Preferences﹥Notifications﹥TV﹥[uncheck Badge app icon], as well as other types of notifications for this app and other apps.

You may need to sign in to the TV app (menu Account), before it registers as an app for System Preferences﹥Notifications﹥. Could that be it?

I can’t think of anything else to try rn. Consider contacting the Apple Support staff for further assistance ( [1] or [2] ).

Unfortunately in Notification Center there is no Apple TV or TV icon to uncheck.

As mentioned, configuration is done in System Preferences.

Even Apple TV once open do not show any details about the notification showed on the app icon

No details on notifications will be shown in the TV app. Notification messages go to Notification Center (under Date & Time in the menu bar in Big Sur).