I suggest you read the threading article and implement for the per folder and the global un-threaded options. https://support.mozilla.org/en-US/kb/message-threading-thunderbird#w_changing-default-threading-mode

There is not much to do with losses when moving files other than right click and select properties and then repair.

Make sure your antivirus is not scanning in the Thunderbird profile folder while the program is running. That and trying to copy multiple messages from IMAP folders to local folders are the two greatest issues with mail loss these days. The antivirus contributes to IMAP losses as well as timeouts can occur in the process while the antivirus fuddles about with it's scanning. Why they think they need to scan an email they just certified is clean or retrieved from a store that they had scanned and decided was clean I do not know. But getting anything that makes much sense from anyone that claims to be "security" is usually a wasted effort. Almost as good as a straight answer from Microsoft of intelligence from the military.

The emails were moved from the inbox on my computer to a folder "attached" to the inbox, the thread option was cancelled and the emails disappeared is what happened.

Forutnately, a check on my webmail later showed the emails were still in the inbox there, so the quirks and incompotencies of Thunderbird 115 were thwarted.

As regards your statement "There is not much to do with losses when moving files other than right click and select properties and then repair", how do I right click on a lost file????

The whole idea of threading may have seemed ideal to the programmers, but the reception of Thunderbird 115 clearly showed that the whole concept of 115 was not ideal for many of Thunderbird's longterm users, including threading. Maybe the programmers could learn from this to keep the core of Thunderbird secure, fast and efficient and let users opt in to changes rather than having to opt out of them.

I have never had problems with anti-virus interfering with my emails and, indeed, IMAP doesn't seem to be the problem here but Tnunderbird does.

I saw a footnote on a page in this forum that posting a correct solution a day could benefit a thousand Thunderbird users. Whether this is meant to be encouraging in some way, I don't know. To me it suggests that there must be hundreds of thousands of Thunderbird users at any one time affected by problems with the product.

I simply do not understand your first paragraph. What has threading got to do with your moving emails?

You right click the folder!

I really do not care what you have perceived to be your antivirus issues in the past or the present. I would guess most antivirus failures are blamed on another piece of software as the problem manifests there, not in the antivirus. This forum is full of folk in denial that their antivirus could be a problem to the point we have canned text and test to lead them to that conclusion. Care to try them out?

For us to better investigate this issue, we will need some more information.

Please provide results for the following test on your system

1. Does Thunderbird work as expected in Thunderbird troubleshooting mode?
2. Does Thunderbird work as expected with your OS started in safe mode with Networking. Instructions for each operating system: Windows 10/11, Windows 8, Windows 7, OSX

Or you might care to peruse the woes in this wiki. I have simply given up updating it with antivirus failures because all it proves is they are a disaster waiting to happen. https://wiki.mozilla.org/Thunderbird:Testing:Antivirus_Related_Performance_Issues

Then you might want to look at the memory diagnostics. Their are applicable to your issue as well https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

If you have feedback, there is a menu item for it on the help menu in Thunderbird. It has no place in the peer support forum.

What you are not going to get is a click this, or set this to stop it happening answer. The cause is a matter of guesswork. You can continue to undertake diagnostics, or you can create some exceptions in your antivirus that will make oyu life easier. It is your choice.

A rambling and irrelevant response. You seem obsessed with anti-virus rather than considering there might be a problem with Thunderbird. End of story.