Have you tried this.

Start your new Thunderbird. Open the help menu and select the more troubleshooting information click the show profile button. Close Thunderbird. Press Atl + Ctrl+Del keys and from the menu select the task manager. Check the list of background tasks that there is no Thunderbird (one of the issues with the copying is the shutdown has not yet fully completed) Close Task manager ( or end the Thunderbird task if one is still running)

Windows file explorer will open in your existing profile. So there is no this is where things might be, it makes sure you and the application are on the same page as to where your profile is..

Now open your old profile data in another file explorer windows and copy the whole lot over the new profile and look for the replace messages to be sure it is actually replacing and not placing the data down a lvel or something. Make sure the copy includes all the sub folders. I have noticed some reports the copy is only replacing the top level files and not the sub folders. I don't know how folks mange to do that so I can't offer a what not to do for it.

Start Thunderbird. All should be there and functioning.

Worked like a charm!!!! Great answer. Thanks!!

My system is Linux, not MSWindows (so a slightly different process) but just WHY should I need to move the profile's files in the first place? I can force TBird to load the old profile with the "--profile .." switch at the command line (and could probably modify the launcher icon on the panel to use the profile path) so I know the profile itself is still good. I edited the "profiles.ini" to only have information on the correct profile, yet next time I start Thunderbird it creates an all-net empty profile.

Used to be when it started this new-profile thing I could just go into the program, bring up the "about:profiles section in the Troubleshooting Information and set the REAL profile to be default (then clear out the extras once TB had loaded the correct one. Now I go into that section and it doesn't even SEE the old one, and instead has created *2* all-new profiles.

Is there something that we should be editing in the old profiles, or perhaps something in the profiles.ini to force it into using the old profile and stop spontaneously creating new ones?

Seems that if you edit the profile directory in installs.ini (and probably the "Installs#######" section of profiles.ini) along with editing the Default entry in profiles.ini, then TB will go back to using your old profile.

It seems the newer Thunderbird version also wipes out your message filters too, in the midst of trying to get your old profile back. Had to pull a copy of my message filters from another machine that hadn't been upgraded to 91.2 yet. That copy worked fine with this configuration (the one where I got the old profile working again). I'll just need to be sure to back up that other machine's profile so I have a reference copy of what I should have (I had been syncing my primary machine's TB profile to the laptop).

I can tell you that my upgrade to 91 completely destroyed the filtering mechanism in Thunderbird. I even tried just renaming msgfilters.dat to start over with no filters, and they still did not work. Other things are broken in my Thunderbird 91 install including the link in message display "always show remote content from..." So in my hands, I am staying on 78, and happened to see this post looking for how to stop Thunderbird from offering the upgrade. :(

Right now I'm running Thunderbird 78 (a binary download for Linux, extracted the .tar.bz2 to a directory under $HOME). It's configured to disable auto-updates and to not download updates, yet it still was nagging that there's a new build available (I might have gotten that to stop finally, will have to wait a few days).

Now, if there were a way to export ALL your TB settings to a file, one that could be imported to a new machine/OS/etc, then a lot of these issues could be solved. Not even something within Thunderbird itself (there's a lot to be said for it being an external utility). You could have it map locations for different operating systems (a bit complex, which is one of the reasons I'd think it would be an external utility). I put that in as a request many YEARS ago.

Nope, It ****STILL**** keeps nagging me to install the latest TB build. But not going to do that for a while until it looks like upgrading profiles works correctly.

I am going to lock this topic as the ongoing discussion is not aimed at fixing the issue raised by the original poster lrlisle. Too the best of my knowledge their issue was solved a month ago and this ongoing posting is nothing but spam as it is not related to their issue.

If the answers here do not fix your problem you are welcome to actually ask a question in the forum seeking support.

@jelabarre59 if you had done some searching on this site you would be aware you can not turn off the update notifications on Linux.

@Roy, I use windows, I have had no issues with filtering post V91. So I guess it is something unique to your system. But I am not even going to try and assist you on someone else topic to find out why you appear to have a problem. Ask a question and have V91 installed so we can do some diagnostic steps if you want support.