Automatically opeining "next" message
I have Thunderbird set up so that new messages are opened in a separate pop-up window. When I read one and delete it, T-Bird automatically opens the next OLDER message in that window. I would want for either the next NEWER message or not open another message at all and just go back to the Message List. How do I do that? There does not appear to be an option in Settings. My T-Bird version is 128.1.1esr
Opaite Mbohovái (2)
If you open the settings and scroll about two-thirds of the way down you'll find the 'Reading & Display' section. In that is a tick-box to "Close message window/tab on move or delete." Ticking that should provide your second choice.
As for opening the next oldest, do you have them sorted with the oldest at the top of the list or the newest? Reversing that may get what you want.
Moambuepyre
To make the next newer message open after deleting, Settings/General, Config. editor, toggle mail.delete_matches_sort_order to true.