See https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

I have no interest in a shouting match. Nor do I personally accept blame for anything.

There is no other profiles, it appears the update has erased ALL previous version data. Congratulations IT wizards.

It is very understandable that you are frustrated to say the least, but please do not use capitals as it implies you are shouting. This forum is manned by fellow Thunderbird users who offer time in a voluntary capacity and no one was involved in whatever occurred.

Thunderbird does not update if you select 'Not Now' at prompt. If it did then everyone including me would be complaining because it would be in the code.

Do you have any updater software operating on computer? I have come across plenty of people who did not even realise they had something else on computer that was controlling the update of Thunderbird.

Some useful info may help understand what has occurred so we can check out what is going on.

What version of Thunderbird were you previously using before the update? What version did it install on update?

Do you store Thunderbird profile in default location? If yes: what do you see in the 'Profiles' folder - (I'm assuming you use Windows OS): C:\\Users\User Name\Appdata\Roaming\Thunderbird\Profiles Post image showing contents of 'Profiles' folder.

As you run a business, I'm assuming you create regular backups of the 'Thunderbird' folder: C:\\Users\User Name\Appdata\Roaming\Thunderbird Please let me know so we can advise on reinstalling.

Do you use IMAP or POP mail accounts? How many mail accounts were in use in Thunderbird? Imap accounts may need to import mbox files from backup into the 'Local Folders' mail account first and then gradually upload to server if required. So it is important to understand your setup.

What Anti-Virus product are you using on computer? Do you have other clean up products installed like CCleaner or WiseCleaner etc ?