Strange icon and yakuake behaviour in HiDPI screen

I have a 4k screen in my laptop. This far only Plasma has been able to scale everything satisfactorily. In other desktops, something eventually goes very wrong in scaling.
Wayland seems to be a mission impossible also, in scaling.
Now also Plasma has problems in scaling. I do not know what causes it. Yakuake’s tab bar is not scaled (it is only few pixels tall) and also some window decorations, such as the close icon in modal dialogs are not scaled.
Previously everything scaled find, but now it is broken as in other desktops.
I cannot understand why this is so difficult. Does anyone else has similar symptoms?