Which is the name of file (or was it a folder?) you copied from where and posted to where? Which instructions did you follow?

probably pasting to ....appdata\roaming\thunderbird instead of to ... appdata\roaming

Thanks both in brief I am following this below: But end up with no prompt???

Ensure thunderbird is NOT running.

Enter%Appdata% - it opens file explorer in Appdata\roaming

Copy to flash drive

New laptop - again - thunderbird is NOT running.

repeat %Appdata% - now in Appdata\roaming foder

copy and paste

BUT no prompt

You should copy the "Thunderbird" folder from your backup and - Thunderbird closed - paste it in....\AppData\Roaming\ here

Thanks Mapenzi ... that is what I have done, honestly - tried about 20 times, even deleted and re-downloaded T/Bird - but when I do exactly what you have said - nothing happens, nada, when I am expecting a PROMPT to override earlier data.

I don't know why you would need a prompt! TB closed, remove your actual Thunderbird folder which is located in Roaming ... users\username\AppData\Roaming\ then copy the entire folder Thunderbird from \AppData\Roaming\ in your backup and paste it in your actual "Roaming" folder. Restart and everything should be there.... but I think there is still some confusion on your side

Confusion - yes, indeed, and my apologies for that. The MUST prompt to be anticipated I am referring to was from an earlier Q&A on here.

Let me try again - and thanks.

You are likely referring to my guidelines. The MUST was included as a reminder, as some people incorrectly were pasting to the appdata\roaming\thunderbird folder. Following my suggested steps, that was because installing and starting thunderbird causes the profile to be created. the transition was to overlay that completely and those who followed the process were successful. You can verify that by installing and closing thunderbird and then browsing the appdata\roaming folder, where you will see a thunderbird folder. A possibility of not seeing that folder occurs when the user installs thunderbird from microsoft, as that release uses a different location for the profile.