See if this add-on helps:

https://addons.thunderbird.net/en-us/thunderbird/addon/deselect-on-delete-tb78/

Thank you. I am not familiar with how to proceed. The link you gave me downloads a *.xpi file. When I double-click the file, it appears to use BreeZip to unzip into 2 files, a *.json and a *.js. What do I do next?

See https://support.mozilla.org/en-US/kb/installing-addon-thunderbird

I added two add-ons, Deselect on Delete TB78 and Select Prev on Delete, and neither one seems to work as described. When I delete an email, the cursor seems to jump at random, sometimes up sometimes down. The description of Select Prev on Delete says "Selection of the previous message (instead of next message - default behavior) when deleting (only for Thunderbird 115 or above)." The default behavior I am seeing in TB115 is NOT selection of the next message.

I wouldn't have both add-ons running. Deselect on Delete works here. To change which message is selected after delete (which is irrelevant if Deselect on Delete is enabled), toggle the preference mail.delete_matches_sort_order to true or false in Settings/General, Config. editor.

I only ran one at a time. I changed mail.delete_matches_sort_order from false to true. Now when I delete an email, the select/highlight goes back to whatever email was previously selected.

There does not seem to be any pattern to what TB is doing. I can get several situations/actions when I delete an email. Sometimes the screen will jump up, sometimes down, sometimes only a few lines, sometimes 20-30 lines, sometimes I can see the selected email on the screen, sometimes it is 2-3 screens away. The program does not work as advertised and both the add-ons you recommended do not work as described. Very frustrating.

Something new today. I have both add-ons turned off. When I delete an email, the highlight moves up one slot. Supposedly the "normal" operation of TB is for the highlight to move down when an email is deleted.

Something new today. I have both add-ons turned off. When I delete an email, the highlight moves up one slot. Supposedly the "normal" operation of TB is for the highlight to move down when an email is deleted.

That is controlled by the preference mail.delete_matches_sort_order mentioned above.

To your previous comment: I have mail.delete_matches_sort_order turned on (true).

Again, something new today. When I turn on the add-on Select Prev on Delete and delete an email, the cursor/highlight moves up two lines, not one.

The action of the add-on is going to conflict with the preference setting, so I suggest disabling the add-on and selecting true or false for the preference.

I've already done that, didn't help. I've backed up my Profile, I'll uninstall and reinstall TB tomorrow. Different question: I have a 64-bit computer but have used 32-bit TB for several years. Should I try the 64-bit version of TB? If so, where can I find it?

There's no reason to uninstall/reinstall the program, but you might find a new profile is worth creating: Help/Troubleshooting Info, about:profiles.

There's no significant performance advantage of 64-bit TB over 32-bit TB. Either one can be downloaded here:

https://www.thunderbird.net/en-US/thunderbird/all/

If I create a new Profile, won't I lose all my emails? Is there a way to save all emails and move them to the new Profile? If so, how?

No mails are lost. In the new profile, adding IMAP accounts will download the existing mail from the server. For POP accounts and mail in Local Folders, copy the mbox files - the large files with no extension, named after folders - from Mail/<popservername> and Mail/Local Folders, and .sbd subdirectories, in the old profile, to Mail/Local Folders in the new profile, with TB closed.

Thank you for the reply: - What are IMAP accounts and POP accounts? Which one do I have? How would I find out? - Where are folders Mail/<popservername> and Mail/Local Folders and where are .sbd subdirectories? I assume in the Profile folder. Under my Profile folder, I have 8 subfolders. TB says <sbidu2z8.default-release> is the "Profile folder". There is a subfolder "Mail" but under Mail, there is no popservername, only Local Folders. In the Local Folders folder, there are no large files, no MBOX files/folders, and no .sbd subdirectories.

A new problem was seen today. This does not happen every time, only some of the time. I try to send an email and get this message: Send Message Error Sending of the message failed. The message could not be sent because connecting to Outgoing server (SMTP) Smtp.aol.com failed. The server may be unavailable or is refusing SMTP connections. Please verify that your Outgoing server (SMTP) setting are correct and try again.

What are the correct settings for the Outgoing server (SMTP)?

Account Settings, Server Settings, Server Type is POP or IMAP. It appears your accounts are IMAP.

For AOL, use smtp.aol.com, port 465, SSL/TLS, OAuth2 authentication, User Name = email address.

TB will not allow me to use smtp.aol.com. When I enter that and move off the field, it changes back to imap.aol.com. Also, TB says the default port is 993.

The incoming server is imap.aol.com and the outgoing server, which you asked for, is stated in my previous reply.

I have no idea what an Outgoing server is, nor do I know what an Incoming server is (if there is such a thing). I simply copied the error message I received. When I follow your instructions and go to "Server Settings", I see "Server Settings", "Server Type", "Server Name", "User Name", nothing about Outgoing.