I've installed another app. Done. I've lost enough time.

re :I never added my gmail account in Thunderbird

You mention a pop up but it would help to see an image of it because it might relate to Email or Contacts or address book.

If it mentions your email address then you added something at some point in the past because it's impossible for Thunderbird to know something like your email address if you never told it.

Did you check to see if anything was stored in your saved passwords ? Settings > Privacy & Security Click on 'Saved Passwords' REmove any lines that mention that mention Gmail.

It would also help to know what OS you use and where you got the installation/download: eg: https://www.thunderbird.net/en-US/thunderbird/all/ or Windows App Store, Flatpak etc

In Thunderbird Settings > General Scroll to bottom and click on 'Config Editor' In search type: gmail Does anything appear that mentions your email address

Hello, thank you for your reply and advice. I finally applied a very simple and radical solution that usually resolves all problems. I simply deleted the application and all data, as well as the folders and traces of the Windows registry, then reinstalled Thunderbird. I configured the accounts and no more problems. Have a good Sunday, if possible.