Hi. You need to activate your old profile to migrate all your settings, accounts, folders, addons etc. Whenever you upgrade Tb to a new version, by default, it uses a new profile. You can change this by going to HELP > TROUBLESHOOTING INFORMATION. Scroll down and look for the link "About:profiles". From there you can activate your old profile and set it as default if you wish.

❗ BEWARE: Using an previously existing profile with a new version of Thunderbird will render it unaccessible on the old version. Should you wish to use your previous version of TB for any reason (i..e. addons not work on the new version), you will not be able to access your profile and will have to create a new one. You are strongly advised to make a backup copy of your existing profile before using it on a new version of TB.

Gio Thank you but this only shows the profiles created on this PC. It doesn't let me access the profiles from my old PC (which isn't working).

Have you actually copied the profiles on old PC and transfered them to correct location on new pc ?

Or if everything was in an imap account and you have created that as new, have you subscribed to see the folders which you have on the server that contain all your emails?

I was able to restart my old computer. The solution is given in Mozilla T support notes: replacing the root directory in the new Thunderbird folder . Thanks for your help.