Perhaps the beta is announcing information from elsewhere.  Try closing Thunderbird while the beta is running.  Then switch to an earlier version. See if you hear announcements in the earlier version.  That will help determine if the beta is not allowing part of the program to close properly or if it is getting information from somewhere else.
Gene
From: Don H
Sent: Saturday, January 09, 2021 8:48 AM
To: nvda@nvda.groups.io
Subject: [nvda] beta 3 and closing programs
I can't specifically say this is a beta 3 issue but only started
happening after installing NVDA 2020-4 beta 3.
I am using the latest version of Win 10 and Thunderbird.  After using
Thunderbird I use alt f4 to close the program.  It appears that
thunderbird closes as it should.  I have thunderbird set to announce new
mail.  The strange thing is that with Thunderbird not open I still get
announcements of new Email which tells me that Thunderbird was not
closed properly when using alt f4 to close it.  Thunderbird is not
showing in the system tray or on the task bar when these announcements
are announced and I must open Thunderbird by using the icon on the desktop.