How to get back notification that new messages have arrived in TB 91

There was always an icon in the system tray (an envelope) that showed if new messages had arrived since the last time I looked at my mail. Now in TB 91 the icon shows unread messages, but does not indicate if new messages have arrived.

The old icon was very useful as I always have unread messages in some of my accounts. Having a count of new messages in the tray icon is not that helpful as it already is shown on the icon in the task bar.

Is there any way to get the notification back? Why was it removed?