I would try and respond, but honestly I don't understand the question.

Perhaps this will assist as the steps cover most issues, not just memory. https://wiki.mozilla.org/Thunderbird:Testing:Memory_Usage_Problems

Personally I find most of the extreme performance issues stem from Third party products. SPAM/Scam toolbars and antivirus programs being my pet hates. They cripple the software often. I recommend an automatic exception for the Thunderbird profile folder in any antivirus product. If you are using IMAP, be aware simply deleting an email involved a round trip to the server and two interferences from antivirus in the process. One on the outgoing request and one on the reply and that does not matter if there is an exception or not. That is about file changes making the files unavailable when needed because they are now locked for scanning after each change. 50 deletions, 50 scans of the base storage file.

Is the program single threaded? Not for years. Just have a look in the Windows task manager.

The unified folder has been with Thunderbird since what version 3 I think. I have never fully trusted it, but many use nothing else. But there were issues with it post the version 115 release and the development team released an addon that can reset the unified folders as part of the debugging process. here https://addons.thunderbird.net/en-US/thunderbird/addon/unified-folders-debugging/?src=ss

Back in September last year when the addon was released the information that came with my email notifying me was"For users who have issues with 115.3.0 or newer, they should be encouraged to use this tool, and file a bug report with the diagnostic output (created before they try to "fix" the issue)." I have no idea if there are still issues requiring bug to be filled, but if you have one I guess there are.

I will use some of your input thanks.

My basic problem is I click on the UI and it gets the click, it selects the item in the inbox listing, highlights it properly, but it never or greatly delayed (a minute) updates the right hand message to match. This seem like pretty easy stuff other than if it has to pull the email from the server but from looking at activity monitor I don't see it hanging there. If it can't take a click and immediately display the email message, like the top 10 items in the list which should be cached if not completely loaded, things are bad.

I will add that sometimes thunderbird just lose the click if it is trying to update the inbox index display and I click on an email just before it starts the update, it completely ignores my click. Seems from what I can see the UI is not getting highest priority.

I'll update if I figure it out what is going on cause this must be specific to me and thunderbird or no one would use it. This is super basic failure. It did not use to have this problem. Trying to figure out what/where something changed is my challenge.

I'm on to your "pet hates" as Bit Defender has magically installed an add-on which if I turn it off, Thunderbird lets it turn it back on. If I try to delete it Thunderbird says ~"you can't" So, we have malware vendor installing malware in my email client and my email client is protecting it and not allowing me to remove it. What a mess.