Unable to Lowering Screen Resolution on kde neon , KDE Plasma for Lenovo Y50

[Ybmyhs]

The default resolution on Y50 is 3840 x 2160. Unable to Lowering Screen Resolution on kde neon , KDE Plasma. When change the value to 1280 *1024, it is no any flicker, response or prompt out message.
The I need to use of 200% scale to read the text.

But the same notebook install kubuntu can change the resolution to any on list resolution. E.g. 1280 1024 / 1920 * 1080.

Please help. I want to try for kde neon for rolling update.
Many thanks.

[oshunluvr]

Try using a resolution that is correct for the monitor - 1920x1080

[Ybmyhs]

Yes. I have selected 1920 x1080. But the screen doesn't changed. Still using 3840. Even login logout, change to x11 or Wayland.