Created attachment 166898 [details]
Screenshot showing the extra border

SUMMARY
Windows which have the new KDE window borders (i.e. any system application, but not something like Firefox that draws its own CSD) will display a 1px wider window border on the left and top, only on scaled displays - Or at least, on my 150% scaled display. On non-scaled displays, the window displays fine.

The extra border is most noticeable on the left, but it is also along the top, and it extends a little to the top-right corner as well, but it abruptly cuts off.

I realise this probably sounds *incredibly* petty, but the 1px extra on the left is surprisingly noticeable. I have attached a screenshot, where you can zoom into the left and see the extra pixel. I have attached a screenshot of Konsole, plese zoom in quite far (i.e. 1600% in Gwenview) to see it better. You can see the border is all the way along the leftm and all the way along the top, but only a little on the top-right, and not at all along the bottom where it is still 1px.

It is my opinion that having a 1px border all the way around the window looks better even on scaled displays, but having a consistent 2px border is probably also ok as long as it extends all the way around the window (I assume one of these is the intended functionality).

STEPS TO REPRODUCE
1. Open a window on a scaled display, or at least, a 150% scaled display.
2. Window decorations have one extra pixel on the left and top only on the scaled display. On the non-scaled display, it is 1px consistently.


OBSERVED RESULT
Window border have 1px extra on the left side, on the top side, and a little on the top-right, but only on my 150% scaled display.


EXPECTED RESULT
Window border sizing is consistent, either 1px or 2px (or some other size), all the way around on scaled displays. The border is consistently 1px all the way around on non-scaled displays.


SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 6.7.8 Linux Zen
KDE Plasma Version: 6.0.1
KDE Frameworks Version:  6.0.0
Qt Version: 6.6.2 

ADDITIONAL INFORMATION
- I am using the Breeze Dark theme.
- Issue is not present when window decorations are hidden, because the border is hidden too.
- GTK applications that draw their own window decorations are unaffected.