Press F8. That key toggles the state.

Matt, that is a supremely useful suggestion for when I want to eliminate obvious or known spam from the inbox message list display. However, my problem involves a feature I mis-named as the "preview" pane-- a pop-up window that appears whenever I simply click on a single message, as in the attached screen-shot'.

So, I searched again for something in the documentation, a feature I could turn off and on, as with your F8 control. Sorry to have been so imprecise about the appropriate term "pop-up" (instead of "preview panel"), and look forward to your comment.

What you want to change is the setting for how messages are displayed. You have it set to show messages in new windows. Apparently, you want them to be shown in the message pane instead.

≡ button > Settings > General > Reading & Display > Open messages in ... an existing message window

That image is of a message in it's own window, but I am left confused as that is an action that should only ever occur post a double click.

To follow Ricks advice,

You will get a change in action on double clicking but not single clicking as you specified.

SO I am left to ponder the issue of a single click. Windows has a setting for this Could it be you have enabled this

There is also apparently an issue with some mice on Windows. I saw HP and Logitech mentioned specifically) that make single clicks into double clicks. (I had never heard of it until I tried Google with the issue tonight) It has become such an issue someone has developed this software to modify how widows manages the mouse clicks. https://apps.microsoft.com/detail/9pdgm7nl2ff2?hl=en-us&gl=CH&ocid=pdpshare

It is apparently free software and the source is available here https://github.com/nenning/DoubleClickFix as well as some basic instructions for use (scroll down past the source file lists)

Good catch, Matt.

Matt and Rick-- thank you!

RE: Click and Double=Click My Logitech mouse driver is a bit flaky, since a single click sometimes yields a double response, as though I had clicked twice.

RE: Pop-up windows. Will check my TB setup for opening each message in a separate window, although I do not recall ever having chosen "open in a separate window".

RE: Why pop-up windows are more than annoying Viewing anything by opening the message is dangerous, considering the more recent attack modes.

RE: Click and Double=Click My Logitech mouse driver is a bit flaky, since a single click sometimes yields a double response, as though I had clicked twice.

Some mouse models have a (middle) scroll button which can also be used for a double-click by pressing it. Maybe you did this inadvertently?

I may understand one of your objectives better now: you don't want any preview because, for privacy or security reasons, you don't want any message to open automatically. A message will open whether you click or double-click on it in the message table and whether you have preferences set to show it in the message pane, a new tab, or a new window. The only way not to open a message is not to click on it in the message table.

If you are not already familiar with the setting not to load remote images, you may want to consider using it.

Rick, My only objective is to have my single selection click on the message (followed by a color bar covering the selected message(s)) not prompt TB to do anything else until my next command. As indicated, my M705 Logitech mouse seems to respond to a click on a message in TB as a double click, as though I wanted to open the message in a new window. Preferably, display of the text or limited graphics of any selected message automatically occurs in the lower screen window (see attachment). As you recognized, I want to avoid activating any scripts by viewing the message in a new window (although recent exploits have bypassed even that measure of safety). For a better idea how I want my TB screen to appear, see attachment below.

Thanks for staying with this, Rick.

>>> Rick, in your comment written 5/0/26 at 6:25am, you clearly understand my objective. When I checked the TB settings for my accounts, the auto-open in separate window behavior occurs in "open in separate window" and in "open in existing.window".

>>> Matt, when I checked the link you sent to deal with my flaky mouse driver, I found the fix works for only W10 and higher, not for my W7 (though I did try to install it, anyway).. When I varied the speed of my mouse click, it did not alter the auto-new and-separate-window-opening behavior.

It was not always this way with TB and W7 Pro 64, so I may need to reinstall or replace the mouse driver. For replacement, I have to find a safe source of a W7 mouse driver for the Logitech M705. On the Logitech site, no downloads are available for the M705 under W7, nor for any other cordless optical mouse of similar description. Strange, and definitely a demerit on Logitech.

BTW, I did check voltage on the mouse's two AA batteries, and found them at 1.22v each, but when I replaced the batteries with new batteries at 1.52v each, it made no difference.