I do not have the answer, but if deleting that file works, it is in your profile. That link you showed was for another person's profile. If you locate your profile at c:\users\<yourid>\appdata\roaming\thunderbird\profiles\<your-profile-name> You will see the global file. Delete it and restart thunderbird. Browsing the text file, profiles.ini in the thunderbird folder will tell you the name of the specific profile. Do post back if that works.

After finding the hidden appdata folder, I got to C:\Users\smb2\AppData\Roaming\Thunderbird\Profiles. (smb2 is my profile) The only folders there are hgp4cw05.personal & yacmgsik.default. Although each has several sqlite files, none are named global-messages-db.sqlite. Any suggestions? Thanks.

Okay, this calls for desperate measures. Now that you know where the profiles are, my approach would be to: - exit thunderbird - copy the above c:\users\smb2\appdata\roaming\thunderbird elsewhere. That is everything you would need in case of a problem to reconfigure profile - uninstall thunderbird - install thunderbird again - start thunderbird - if it picks the profile as desired, you're done - if it presents screen to create email account, it somehow didn't see the profile. so,

  - exit thunderbird 
  - copy the backed up thunderbird folder back to where you copied if from. windows will prompt that it will replace files. that's ok

- now restart thunderbird and all should be there.

Thanks again for your time with this; problems continue. When I tried to uninstall, there were 2 versions of TB, with the following results (neither could be uninstalled):

Mozilla Thunderbird (x64 en-US) 462 MB 115.12.1 6/22/2024 This led back to the reboot loop ("Your computer must be restarted to complete a previous upgrade of Thunderbird. Do you want to reboot now?").

Mozilla Thunderbird (x86 en-US) 439 MB 115.3.1 10/1/2023 This generated: "Windows cannot find 'C:\Program Files (x86)\Mozilla Thunderbird\uninstall\helper.exe'. Make sure you typed the name correctly, and then try again."

What's next?