When I receive an email in thunderbird I know I won't read (an advertisement for instance), that should be useful to delete this mail directly from the notification that appears on top of the screen (see this screenshot showing such a notification)
I'm returning to Thunderbird after many years' absence and I'm impressed with all the improvements and how good it looks and functions. My immediate reason for returning was the fact that Comcast Webmail did not support sound notification or any notifications, for that matter.
So, yes, after quickly getting used to the presence and value of notifications, I would definitely support the addition a "delete" option to the popup notification.
One suggestion for improvement: After selecting the Delete option from a notification in MacOS opens the Thunderbird app window, which disrupts workflow. It would be great if this behavior could be eliminated.
As has been noted this is available, as of release version 138 / ESR version 140 , via https://bugzilla.mozilla.org/show_bug.cgi?id=1482172. There are a couple bug still to be resolved that are linked in that bug report.
If further improvement is desired, please create a new idea.