Are you really asking how to disable threading?

I suggest you try reading the support document that explains how to disable the threading,.

As for the missing piece of expand all and collapse all. They are on the traditional menu bar.

That helps somewhat.

If I select "threads > all" then I get this after selecting Date > Descending. The dates are screwy instead of having *individual* emails shown on their original received date.

The intent is to show ALL emails singularly (not collapsed) and on the date they were originally received. This seems to be the only folder this happens in.

When you get older (you're young) you'll understand how hard it is to get things to consistently show the way they used to 20 years ago. don't know where that 'support document' regarding disabling threading.

This is the official (to my knowledge) documentation. Well worth the read https://support.mozilla.org/en-US/kb/message-threading-thunderbird

Here is my own documentation on threading, duplicating the above, but it may help: You need to highlight each folder and click View>sort by>unthreaded. If this applies to just a few folders, just repeat the process as necessary. If you have many folders or plan to add many new folders, you may wish a different approach, below:

More info: To change default for *new* folders, In config editor, you can change default that applies to NEW folders you set up: mailnews.default_view_flags 0=unthreaded

Config editor is available at Tools>settings>general and scroll to bottom right.

 ------------

To set many *existing* folders, follow these steps: (I creates a crude video that walks through the steps. The video was created with table view for the message list pane.

   https://davidkirk.org/SettingDefaultFolderView.mp4  that demonstrates the following steps:

   First, highlight a folder that you have set to unthreaded	
   In the Message List view, in the column header, on the far right, open the options button that shows    
    context menu. :
   At the very bottom is the option:
   -> "Apply current view to..."
   -> "Folder and its children..."
   -> Hover over an account
   -> In the next menu don't select a folder. Instead select the account name itself.

ALSO, for future installations of Thunderbird, 
- install Thunderbird and exit prior to setting up accounts
- 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);
- copy the user.js file into the profile
- now, when you start Thunderbird, unthreading will be the default. Problem solved. 

Thanks David, that helped. I did read that document you referenced. When you're 60+ y.o., you don't remember or aren't familiar with all the latest lingo 'threaded' and your mind just thinks 'how do i *expand* this?' Just a suggestion to other code writers so they will maybe quit changing terminology; they'll find out in 20 years! :)

On the side, one thing that frustrates us seniors is having to type a new password in TWICE, then. . . .typing in the little dots withOUT knowing what we're typing. Our fat old fingers can't be assured to type what we're thinking. Wish someone would quit it with those stupid dots already; just show me what I'm typing. The eyeball helps but there's no one looking over my shoulder or I wouldn't type my password in; they fortunately haven't caught on to making me type my account name with little dots as that info is just private as well.

When might Tbird give us the option to put the File/Edit menu back above the Write/Reply... menu as it used to be pre-115 version?

Thanks again for the threading help though!

That File/edit menu is still around. You can press the alt key or F10 and when it appears, click View>toolbars and tick menu bar. And you're smarter than you think you are. There are many people who wouldn't know to make the post you did. Don't beat yourself up too much. I think you're right there with the rest of us, sharing the same frustrations as the rest of us. Computers - and email clients especially - are complex. I have this strong belief that working with computers keeps our minds involved in problem-solving, and that helps keep us involved with the world. That's our silver lining.  :) Yes, I agree about the dots and typing without seeing, but the internet was devised in a simpler, trusting, time. Passwords and two-factor authentication are the norm now.