Created attachment 132527 [details] Minimal screenshot of the problem Steps to reproduce: Press Super+P to call up the Extend display popup. The popup appears. Actual result: The popup has a big portion of unused space on its right margin. Attached screenshot was made on a laptop on an external 1280×1024 display, which is just big enough. The popup looks the same primary 1920×1080 display.
Recently fixed by Carson Black with https://invent.kde.org/plasma/kscreen/-/commit/49c5d9c5db553a745534099484a6f3e7c6b7bcf4 in Plasma 5.21!