Here is the link for moving a profile in Windows when installed in default location:

https://support.mozilla.org/en-US/kb/moving-thunderbird-data-to-a-new-computer

here is the info in brief steps:

1. ensure thunderbird is NOT running on old machine
2. enter %appdata% in search window on task bar and press Enter key
3. this should open windows file explorer in Appdata\roaming folder
4. highlight the Thunderbird folder and copy to external media
5. ensure thunderbird is installed on second computer, started once and NOT running
6. enter %appdata% in search window on task bar and press Enter key
7. you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there. This may prompt to overwrite an existing folder of same name. allow it
8. start thunderbird and all should be there

Thank you for the reply. These are the steps that I have taken, multiple times. The install version that I can download to the destination computer is version 143, but the source computer has version 140.4.

When I open Thunderbird on the destination computer, it says "You have launched an older version of Thunderbird". Even when I downloaded the 140.4esr version, it still doesn't work. It keeps creating a new profile folder, but not opening the existing profile. Any help is appreciated. Thank you.

Puzzling. The error message sounds like the two PCs are the reverse of what you posted. Somewhere, there is a step being done that causes this problem. Let's start over. - Delete the appata\Local\THunderbird folder on new PC = Delete the appdata\roaming\thunderbird folder - download and install a current version from thunderbird.net - start thunderbird once and exit 0this creates the dummy appdata\roaming\thunderbird folder - NOW, repeat the steps I posted. (DO NOT copy the appdata\LOCAL\Thunderbird folder)