I am not familiar with such a folder, but it sounds like in might be an MS exchange error folder, but why they would show it in Thunderbird I have no idea.

Right click the account in the folder pane and select subscribe. unsubscribe for the folder you do not want to see.

I don't use MS Exchange. The folders don't appear when I access outlook.com directly, so it's not an Outlook problem. There was an earlier posting about this same issue and no solution offered beyond what I did, post with further info about my system settings.

I don't use MS Exchange.

Yes you do use MSexchange, that is what powers the whole hotmail/live/outlook/office365 mail thing. Microsoft only make and support one mail server software. That you are ignorant of a fact does not make it any less a fact.

The folders don't appear when I access outlook.com directly,

You are not doing that at all! You are accessing a website that displays mail data it gets from the mail server in any way it likes. In many regards Thunderbird also does that. Because both are mail clients, except one is a webpage and one is a product installed on your computer that is bound by the strictures of the IMAP mail protocol. The Outlook web site has no such limitation, because it uses Microsoft proprietary protocols to do just about everything it does. No open standards compliance required at Microsoft.

so it's not an Outlook problem.

Such closed thinking is most unlikely to get a result that you might consider a solution.

There was an earlier posting about this same issue and no solution offered beyond what I did, post with further info about my system settings.

Is there some point to this part of your posting? You provide no link for me to have any idea if it is even relevant to this discussion.

But what the, I will go over to google and look for the issue there without the blinkers of demanding the issue is not Outlook and is Thunderbird. Ohh look of found an article at Florida state university from 2021. It appears to me they are created by Microsoft Outlook, I guess the desktop or mobile app, but as I really use neither I do not know. I can only speculate how they came into existence. https://servicecenter.fsu.edu/s/article/What-do-I-need-to-know-about-the-authentication-certificate-used-for-FSUSecure-and-eduroam-1600352706829

Here is another article form a communications company that attempt to explain it to outlook users. As far as I can ascertain it has nothing to do with Thunderbird. https://support.intermedia.com/app/articles/detail/a_id/12123/~/what-is-the-outlook-synchronization-log%3F

Perhaps the earlier posting you refer to was from someone that was determined it was a Thunderbird issue, so restricted their thinking to Thunderbird and missed the elephant in the room because of it.

Reading in the later article, it appears that the folders are created by outlook locally, so I would guess someone has done an import from outlook somewhere along the line here.

Now to your point about deleting folders. IMAP has strong rules about this. Fundamentally the server will simply not delete some folders and they are transmitted to the IMAP client as folders that can not be deleted. These usually show up in Thunderbird interface a folder names in italic. For example the following image the [Gmail] folder can not be deleted.

Likewise you usually can not delete folders that contain mail, or in the case of these folders logs I guess.

So is the folder name in italics? Does it contain anything?

Is there some reason you need to act like such a d*ckhead? But thanks, you did clear this up for me. You'll get further in life by dropping the superiority attitude.

Is there some reason you need to act like such a d*ckhead?

You drove me to it.