When I use the Displays application to change the scaling of either of my screens (2k and 4k), it changes both of them. If edit .config/kdeglobals and set scaling to 1, eDP-1=2 (4k screen) and DP-1=2 (2k screen), then reboot, it doesn't appear to use the specific setting for the screens and only uses the global setting on both.

I thought that this was a limitation of Xorg, but I switched to Wayland and the results are identical.

How do I get different scaling settings working?

Apparently this is a feature of Wayland that has yet to be implemented.

https://bugs.kde.org/show_bug.cgi?id=222428