In spite of following articles here

What articles? Please provide a link.

After logging into User:Del, when dragging the profile from a backup on a flash drive into the Library/Thunderbird/Profile folder, it did not work.

It is entirely unclear what folder you dragged and to where. Please provide exact folder names and the entire (absolute) path.

I followed knowledge based direction and uninstalled Thunderbird. Then I reinstalled it.

You're wasting your time. Thunderbird saves personal information such as messages, passwords and user preferences in a set of files called a "profile", which is stored in a separate location from the Thunderbird program files. So you can re-install Thunderbird as many times as you want, it won't change a thing with your problem at hand.

Sierra asks you to set up a new account.

How is that related to Thunderbird?

I did, minimally, and tried to paste in all of the contents of the old profile into the new profile folder (of a different name).

When copying over the contents of the old profile to the new profile, the whole idea is that you don't need to set up any accounts manually, not even 'minimally' (whatever that means).

I did restart the computer a couple of times and checked terminal to see if the profile shows up.

I have no idea what you expected to see in the terminal.

This is the article I started with: https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

Then I clicked on the article on locating your Thunderbird profile. I held down the option key, clicked Go in the top menu bar and found the file in the Library/Thunderbird/Profile folder. I copied just the d7ehr014.default folder and saved it to a flash stick.

There are 2 Users on the new iMac, Delilah and DR. All of my files and apps are in User Delilah.

I logged into the User called Delilah, clicked Go/Library/Thunderbird/Profiles. I dragged the folder d7ehr014.default from the flash disk into the Profiles folder on the iMac. The Profiles folder had a new Profile, Ilzzyyzv.default already in there which does not contain my files. See attached screen shot.

Note: The new profile had been established when I first opened Thunderbird under the User, Delilah and expected to see my files. Instead, a popup window asked me to either set up a new account or use my existing account. I clicked to use existing. Then it started downloading all Inbox mail, but I could see that my Saved files were not in the sidebar and closed out the app.

Then I deleted the Ilzzyyzv.default folder. When I launched Thunderbird, I got the Profile missing message (screen shot 2).

Then based on the article below with directions to Restore a profile backup/Restoring to a different location/If the profile names do not match, I copied all of the files in d7ehr014.default folder on the flash stick into the new Ilzzyyzv.default folder, overriding what was in there. I clicked over write when the mail folder with my contents popped up. I based this on this article: https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data

I can see that my Saved folders are in the Ilzzyyzv.default folder but they do not show when I open the app. Clicking Tools/Saved Files comes up empty. Nothing in View shows them.

Lastly, when I log into the other User: DR, I can open Thunderbird with all of my Saved folders. That profile works and lives in that User on the new iMac. I don't know how to transfer it to the new User, Delilah. My goal is to get Thunderbird working in User Delilah and delete User DR so that I only have one user.

I hope that clarifies the issue. Please let me know if you need more details. Thoughts? Solutions?

That was pretty clear, thanks.

Then based on the article below with directions to Restore a profile backup/Restoring to a different location/If the profile names do not match,

This is the correct procedure.

I copied all of the files in d7ehr014.default folder on the flash stick into the new Ilzzyyzv.default folder, overriding what was in there.

You'll need to copy over the entire contents of d7ehr014.default, i.e. files and folders, not just files.

overriding what was in there. I clicked over write when the mail folder with my contents popped up.

You may also delete everything in Ilzzyyzv.default (the target folder) prior to copying the stuff from d7ehr014.default (the source folder).

Just in case, can you also post the contents of profiles.ini?

I had selected all files and folders when I dragged them into the new profile. I can't open the profiles.ini to see the contents.

However, before posting this reply, I just took your suggestion to delete everything in the target folder first and then paste everything from the source folder. That worked!! Thank you! Thank you!