Laptop Monitor HiDPI Scaling not working in KDE

[DJViking]

My Laptop monitor has very low HiDPI. I am unable to scale it in “Display and Monitor” setting using Global Scale.

> env | grep SCALE
QT_SCREEN_SCALE_FACTORS=eDP-1=1;HDMI-1=1;DP-1=1;DP-2=1;DP-3=1;DP-1-4=1;DP-1-5=1;HDMI-1-2=1;

> xdpyinfo | grep resolution
resolution:    96x96 dots per inch

When I connect an external monitor the scale is just fine on that monitor, but not the laptop monitor. The external monitor is connected with USB-C.

Laptop: 38402160
External: 38401600 (Ultra Wide)

But when I connected the laptop to an 3480x2160 external monitor, that external monitor also got no HiDPI scaling.

[deano_ferrari]

Are you using KDE Plasma X11? Per-output HiDPI isn’t supported by X11, so Plasma falls back to 96 DPI when mixed-DPI monitors are connected.

[DJViking]

KDE Plasma and X11

But HiDPI does not work either when I have no external monitor connected - only the laptop screen.

I see some recommends switching to Wayland - but is that stable enough now?

[deano_ferrari]

I’ve found Plasma 6 Wayland to be extremely stable. Evaluate it for yourself. It’s easy enough to switch to the desired session from the login screen.

[knurpht]

I switched to Plasma Wayland on TW when I bought my current workhorse. IME it is already better than X11 is many aspects.

[DJViking]

Just tried Plasma Wayland. Works just fine so far - and it scales my laptop monitor.
One little thing though. My VPN Client (BIG-IP Edge F5 VPN) does not scale, and its window is tiny.

[deano_ferrari]

That’s to be expected by X11 applications. They can behave unpredictably with scaling depending on how they were built. In Plasma Wayland, there’s a setting under Display and Monitor > Display Configuration > Legacy applications (X11) where you can choose to let X11 apps scale themselves or be scaled by the system. Try experimenting with that for your VPN client to fix the tiny window issue.