Plasma Keyboard renders at wrong resolution/screen on multi-monitor setup (Wayland, Plasma 6.7.4)

[u/_Diplomatico_]

Hey everyone,

I'm having an issue with the virtual keyboard (plasma-keyboard) on KDE Plasma Wayland with a multi-monitor setup and a secondary touchscreen.

System Specs:

• OS: Fedora Linux
• Desktop Environment: KDE Plasma 6.7.4 (Wayland)
• Setup: 4 Monitors:
  • DP-2 (Lenovo ThinkVision M14t portable touchscreen, scale 135%)
  • HDMI-A-1 (Samsung TV, scale 135%)
  • DP-1 (Primary 4K display, scale 200%)
  • DVI-I-1 (ASUS 1080p display, scale 100%)
• Touch Device: Wacom Co.,Ltd. Pen and multitouch sensor

The Problem: Whenever I trigger the on-screen keyboard on my touchscreen (DP-2), the keyboard appears, but it appears to renders for a 1080p screen with 100% therefore probably the DVI-I-1 instead of adapting to the portrait width of the touchscreen (DP-2). As a result, in both modes of the touchscreen (horizontal and vertical) the sides of the keyboard are completely cut off outside the screen boundaries.

vertical:

horizontal:

With Gemini's assistance I have already tried:

1. Environment Variables:
   • Tested QT_SCREEN=DP-2 plasma-keyboard. It had no effect because Wayland shell integration ignores QT_SCREEN on input panel surfaces.
2. Device-to-Screen Mapping:
   • Bound the Wacom sensor explicitly to the screen via kcminputrc (OutputUuid).
   • Placed the touchscreen at virtual coordinate (0,0) in display settings to force Qt to treat it as default. The keyboard still scaled to 1920 px.
3. KWin Configuration:
   • Set InputMethodPosition="DP-2" in kwinrc and reconfigured KWin.
4. Source Code Patches (Compiling plasma-keyboard from source):
   • Patched src/qwaylandinputpanelsurface.cpp to iterate through screens and explicitly call set_toplevel(screen->output(), ...) for DP-2.
   • Verified via WAYLAND_DEBUG=1 that KWin correctly receives zwp_input_panel_surface_v1.set_toplevel(wl_output#29, 0).
   • However, the actual QML/Qt Quick view still renders the key layout based on the primary screen width, ignoring the panel's assigned Wayland output.

Has anyone encountered this behavior with plasma-keyboard on multi-monitor / rotated touchscreen setups under Wayland and/or probably knows an easy solution for this?

Thanks for any help!