Can't get old folders/passwords after new installation on new Windows11 machine

It may help to know, in detail, how you copied the profile. Thank you

Thanks for helping out. I just copied the folder using Windows Explorer. I pasted it (ipqy1vrj.default) into the Profiles folder, replacing the two that the new installation already had (3hojvnk.default and gg96senm.default-release). Thunderbird wouldn't even start. It only gave a failure message.

Yes, that doesn't work. When copying via windows file explorer, you must copy and paste the entire Thunderbird folder, not just the profile. That is why thunderbird won't start. if the old computer is still available, here are the steps:

BACKUP

1. ensure thunderbird is not running on old PC
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

RESTORE

1. ensure thunderbird is installed, run once, and NOT running on new PC
2. enter %appdata% in search window on task bar and press Enter key
3. delete the thunderbird folder
4. you should be in Appdata\roaming folder , copy&paste the exported Thunderbird folder there.
5. start thunderbird and all should be there

Thanks again. I'll give it a try. Exactly which folder am I copying? Roaming? Thunderbird? Profiles? Will I be losing all the emails I have received and saved since this debacle started?

On the basic question, the folder to copy is the thunderbird folder. BUT, hold off. I presume you use POP account and the normal transfer procedure would overwrite whatever you have downloaded. It may be safer to extract only what is missing. Please state explicitly what is missing and salvaging may be safer for you. Let me know.