[Correction] - it is shame that is impossible to edit post.
OBSERVED RESULT
close button placed at the left top corner of preview window

One request per bug report please; see https://community.kde.org/Get_Involved/Issue_Reporting#Multiple_issues_in_a_single_Bugzilla_ticket

The close button icon is determined by the icon theme, and it's intentional that the current Breeze appearance of the icon doesn't have a red background; we decided, after much deliberation, to choose the simple black X for many reasons; see https://invent.kde.org/teams/vdg/issues/-/issues/62.

The position in the tooltip is also intentional, I'm afraid. We don't want to make it too easy to accidentally close windows.

(In reply to Nate Graham from comment #2)

> The position in the tooltip is also intentional, I'm afraid. We don't want to make it too easy to accidentally close windows.
Sorry, I didn't mention I use vertical panel placed at the right edge of screen and if close button would be placed at the right top corner I would have shorter way to close button. But according your/KDE team opinion this leads to accidentally click into close. I don't agree with that.

In my opinion close button even would be placed at the right top corner  (so close to panel) wasn't be easy accidentally use it, just because user would to have to do two move: left and up. Only one difference with current solution is that user now must move mouse further to arrow would achieve close button at the horizontal position.
Even if mouse is placed in top of icon (placed on taskbar) also user must do two move. In other words user must to do always two move, so I don't understand how is possible accidentally click into close.

Second thing is that when user move your mouse to close button (placed on another side of window view) other windows on the screen blinking. I mean that when mouse over thumbnail then window is raised and all other disapper, when mouse achieve close button, then back all other windows are visible. I'm not sure if this is nice experience for user. Having close button close to panel we are able to avoid such not so nice experience.

(In reply to Piotr Mierzwinski from comment #3)
> In my opinion close button even would be placed at the right top corner  (so
> close to panel) wasn't be easy accidentally use it, just because user would
> to have to do two move: left and up.

Not with thumbnails disabled, where the close button often appeared right where the mouse cursor was. 

(And I think it can also happen with thumbnails enabled depending on the exact positions; but I don't have thumbnails on and my right-edge experience with thumbnails on is limited) . 

> Second thing is that when user move your mouse to close button (placed on
> another side of window view) other windows on the screen blinking.

This is a separate issue of the highlight window effect being too eager to activate; this is in the works with https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/2816

The problem with relocating the close buttons based on panel position is that we would then get bug reports that the close button position didn't match window close button position. Also, for top panels, we'd have to move it to the bottom of the tooltip, which would look quite odd.

This is one of those cases where there just isn't a solution that works universally, and it's way too minor and fiddly to offer user configurability for.

(In reply to cwo from comment #4)
> (In reply to Piotr Mierzwinski from comment #3)

> (And I think it can also happen with thumbnails enabled depending on the
> exact positions; but I don't have thumbnails on and my right-edge experience
> with thumbnails on is limited) . 

I tested this with left and right edge and wasn't able to achieve close button very close to mouse cursor to click it accidentally
 
> > Second thing is that when user move your mouse to close button (placed on
> > another side of window view) other windows on the screen blinking.
> 
> This is a separate issue of the highlight window effect being too eager to
> activate; this is in the works with
> https://invent.kde.org/plasma/plasma-desktop/-/merge_requests/2816

Yes, but as I said "Having close button close to panel we are able to avoid such not so nice experience.", so in this way issue could be fixed and blinking would be happen only after deliberate operate of user (move mouse cursor over thumbnail).

(In reply to Nate Graham from comment #5)
> The problem with relocating the close buttons based on panel position is
> that we would then get bug reports that the close button position didn't
> match window close button position. Also, for top panels, we'd have to move
> it to the bottom of the tooltip, which would look quite odd.
Sorry, do you receive such bug reports now?
Consider please that when we have panel at right edge of screen close button is no placed at "right place" (settings of default window decoration theme), so at right-top corner, only at the left-top corner.  When we have panel at the left edge or at the botton, position is like in default settings of window decorations, so right-top corner. I didn't test top edge, but I suppose here is also placed at the right-top corner and not at bottom of preview of window, because as you said: it "would look quite odd."

Second thing is that some themes for window decorations positioning close button also at the left side, so here user also could report issues like "close button position didn't match window close button position"

 
> This is one of those cases where there just isn't a solution that works
> universally, and it's way too minor and fiddly to offer user configurability
> for.
Sorry, do you mean that better user experience in case of close window is minor? For me such thing strongly improve speen of close window and at the same time user can also avoid not nice blinking of windows.

Why do you want to have universally? Two options could be compromise (or only one switcher):
1. Close button placed as now  
2. Close button placed close to the panel
User could chose what he prefer. I think users migrating from Windows 11 would be happy.

Anyway. I found such feature (close button placed at right-top corner of window preview when I have panel at right edge of screen) in Windows 11 and consider it as very useful and making closing window more efficiently solution.

Please don't re-open closed bug reports. I already provided an explanation for why this isn't feasible for us to further change.