Threads is a toggle that can be switched off using the toggle icon

Ahh… I was wondering why I was seeing so many questions lately asking how to remove threading, because I'm used to change that setting using the View options, but now I'm starting to think what's happening is that many users click that icon, not knowing what it does, and see the effect later when they no longer associate the threading with having clicked that icon…

Thanks for those replies, but there's a different layout for my Linux version.

On the inbox heading area I don't have a second line for Subject and Correspondents.

The only icons are Quick Filter and Sort. There's none for Threads.

In View > Threads, there is a check for All which I cannot remove. Same situation with Sort > Sort by > Threaded.

So I'm still stuck.

A list of Thunderbird's Keyboard shortcuts can be found by searching in the top right search window on this page.

They're located at https://support.mozilla.org/en-US/kb/keyboard-shortcuts-thunderbird.

See if they work with Linux - there are numerous ones to deal with threads.

there's a different layout for my Linux version

That's because of different view options, not because of different OS.

On the inbox heading area I don't have a second line for Subject and Correspondents.

You're probably using Card View instead of Table View:

https://support.mozilla.org/kb/getting-started-thunderbird-main-window-supernova

In View > Threads, there is a check for All which I cannot remove. Same situation with Sort > Sort by > Threaded.

It's in View > Sort By. Can't you choose Unthreaded instead of Threaded there? That option should be available in both Card and Table views…

The following article describes threading in Thunderbird:

https://support.mozilla.org/kb/message-threading-thunderbird

Thanks to both for your replies.

@DavidGG - Yes I've got that now. Thank you.

But it still doesn't resolve my issue. I found that Sort By > Unthreaded still means I have to individually reset every folder.

Also, since TB suddenly started threading everything I am looking for the same master switch which will swap everything back in one hit.

And also I need a means of making unthreaded my irrevocable default.

The article I linked in my previous reply explains both how to apply the change to other folders and how to change the default threading mode. Applying the change to already existing folders may require switching to Table View first, though, I don't know if there is a way to do that when using Card View…

EDIT: Aaand the default seems to be Threaded mode, so that must be the reason this question keeps popping up…

@DavidGG Thanks, I have switched to Table view and the only solution I can see is to individually unthread each folder.

Well, Ok that will only take me 10 to fix. But how many more times will I have to do that? TB has switched itself into threading before.

Somehow there's code inside TB that triggers every folder at once. But I don't have access to this switch and have to fix each folder individually.

I would like a way to permanently and overcome these thread glitches.

Advice on doing this in Linux Mint would be greatly appreciated.

Erm… As I said in my previous reply, the article I linked explains both how to apply the change to other folders (without having to do that one by one) and also how to change the default setting (so new folders you create already have threading disabled)… Did you miss that part of the article maybe?