I saw a flyby comment from one of the developers that downgrading for 92 profiles is not possible. but I would give it a try and see if that is really so. Install the release version and make sure that it installs in a different location to the beta version so you have both. Run your new install but don't create any accounts. Go to the troubleshooting information on the help menu and locate the show for the profile and open it. Close all instances of Thunderbird Now open the existing profile folder in file explorer and copy and paste everything from your old profile folder to the new one. Start your release version. If it worked out all the information will be there.