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Thanks!!!! That worked!!!!

You're welcome. Some people love threads, some hate them. :) (I hate them...)

The problem is.. the fix only works until the next update and then it reverts. I've recently changed to a new laptop, the old one ( still in operation ) doesn't have the threading problem and I've never had to set it. The new install has the problem and it drives me mad, same op system same version of Tbird so why?

I haven't seen that, as the setting is individually stored in each folder's msf file, not one central place. Thunderbird prior to ver 102 (which was released in summer of 2022), UNthreading was the default. For future setups, to start with unthreading as the default, do this:

Create a simple text file with name of user.js with these lines:

    // Set default threading to UNthreaded  ###   <== this line is optional, just for documentation
   user_pref("mailnews.default_view_flags", 0); 

Next,

1. install Thunderbird and exit prior to setting up accounts
2. copy the user.js file into the profile
3. now, when you start Thunderbird, unthreading will be the default. Problem solved.

Thanks David!

User.js worked after unable to uncheck or disable thread!

Want to know if Thunderbird add mouse Gesture feature in this app? I use a lot and it save and quick command in either Edge and Chrome Browser.

I've been a Thunderbird user for a very long time. The only feature that makes me MAD is threading. I cannot turn it off universally, and I think that is a very poor choice. I don't know the technical side of this idea, but the option should be offered if at all possible. I would be much happier and I would increase my occasional contribution to Mozilla if this suggestion gets adopted.

I have provided the indepth procedure so often that I'm tired of repeating it. Get the monthly release, 136, and there is an easy fix at settings>appearance. Yes, it can be turned of universally. Look for my seemingly infinite detail posts on this. It's a few steps at most.