That sounds unusual. If the profile worked in another thunderbird, then it will work here. My guess is there is a difference in version numbers and there may be a compatibility.ini file that could be deleted. Your current problem is that you moved the default profile, so when thunderbird tries to start, it's not there. I would place the thunderbird folder back in place and try again. If you get an error message, please post it. here are my normal steps:

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 WILL prompt to overwrite an existing folder of same name. allow it

#   start thunderbird and all should be there 

HOWEVER

If your backup is just the profile itself, then do this:

1. install thunderbird on new pc, downloaded from thunderbird.net
2. in receiving PC, click help>troubleshootinginformation
3. scroll to 'profile folder' and click 'open folder'
4. exit thunderbird
5. now, paste contents of exported profile, overlaying contents of profile.
6. if there is a compatibility.ini file, delete it
7. restart thunderbird

Thanks David. Let me rephrase my problem. I simply want TB to do a fresh start on a new profile.

I haven't used it for email on this instance for several years. (I do use it on my Win 11 instance.) And the POP and IMAP folders in the default profile would need to be dropped or changed radically anyway since cox.net was rerouted to yahoo last year. So a clean start would be fine. I had uninstalled TB when the problem first arose, and now moved the default profile elsewhere. But now do I need to also delete more of the folders under AppData?

Delete %appdata%\Thunderbird and then start Thunderbird. It should see a brand new installation.

Thanks Matt. That's what I needed.