This relates to Thunderbird 128.2.0esr (64-bit) running under Windows 10 Pro.

Upon receiving new mail messages in a Unified Inbox, the Thunderbird logo with a red dot properly pops up in the Notification area per the attached screenshot, and the Inbox title in the Windows tray also shows the correct number of new messages. Reading or deleting these messages will either reduce the boldface entry or remove the message from the message pane, but the red dot notification icon and new message count persists. The only way to clear these seems to be to expand the Unified Inbox to show all email accounts, and then simply click sequentially on the account names until the notification drops from the Windows tray. Is this a bug or normal operation?