You can turn on Do Not Disturb ("DND") mode to prevent distractions or notifications during specific timeframes.
Schedule Do Not Disturb
On your Mac, choose Apple menu > System Preferences or open "System Preferences" directly from the icon.
Select "Do Not Disturb" at the top of the sidebar.
You can stop notifications ...
Apparently this is a known issue.
I stated "Thunderbird … (updated to latest)" - BUT I was mistaken! The Update only updated to a version of 60. There seems to be no Update option.
There is apparently a version of 68 which does NOT have this problem BUT disables most of my Add-ons.
It seems I have a choice of displaying unread email OR working Add-ons (...
There is no way.
When you swipe right on most notifications, there are the three options Manage, View, and Clear/Clear All. Manage is the one we are worried about, as it can permanently stop notifications.
Swiping right on the Do Not Disturb notification, though, only reveals two options, View and Clear. This shows there is no way to permanently disable ...