This works: https://support.mozilla.org/en-US/questions/1438626

Ok thanks. I had done this a long time ago, and it seemed to work (I just got annoying notifications about updates being available all the time). But then all of a sudden it updated anyway. I think that I know now, why. I updated my System to win 11 and came back to win 10. Maybe, that by doing this, some things didn't go back 100% to what they were before. So the updates came back. Changing the registry didn't help. I hope this will help now. Thanks.

What's the security app? Some, like Norton, have 'software updater' options that perform updates independent of the software's setting.

re :Why does Thunderbird keep updating without my approval and without even asking?

If you want Thunderbird to check, but not update until you click on the 'Update' In Thunderbird you would need to set up: Settings > General Scroll down to 'Updates' section Select 'Check for updates, but let me choose whether to install them' Uncheck - 'Use a background service to install updates' - this will force Windows to ask your explicit permission to perform the update - a sort of double check, so if you clicked on Update in Thunderbird and changed your mind, you can still refuse it.

Be wary...many computers have 'Updater Software' programs which can auto search for and perform updates on various installed programs. Please check....I would strongly advise you exclude Thunderbird from any Updater Software - let Thunderbird be in control, so you have greater control.