Sluggish/laggy UI on Arch Linux + KDE Plasma + Wayland + NVIDIA (X11 slightly better, WebKit env vars do not help)

[pavle99]

Pre-Submit Checklist:

• I have searched existing issues
• I am using the latest Portmaster version shown in the UI
• I tested multiple launch/workaround env vars before reporting

What happened:

Portmaster UI feels noticeably sluggish/laggy/buggy on Linux in my setup.

The app starts and connects normally, but the UI feels slow to render/interact with. It is not completely broken, but it feels janky and less responsive than expected.

I noticed that launching with GDK_BACKEND=x11 changes the UI behavior slightly (in a good way), but it is still sluggish. This makes me suspect the issue is related to the Linux WebKitGTK / KDE Wayland / NVIDIA path rather than Portmaster failing to start.

What did you expect to happen?:

UI should feel smooth and responsive on a high-end NVIDIA system.

Environment:

• Distro: Arch-based
• Desktop: KDE Plasma
• Session: Wayland
• GPU: NVIDIA GeForce RTX 4090
• Driver: 595.58.03
• WebKitGTK: webkit2gtk-4.1 2.50.6-1
• Portmaster UI version: 2.1.7

Graphics info

glxinfo -B:

name of display: :0
display: :0  screen: 0
direct rendering: Yes
Memory info (GL_NVX_gpu_memory_info):
    Dedicated video memory: 24564 MB
    Total available memory: 24564 MB
    Currently available dedicated video memory: 22055 MB
OpenGL vendor string: NVIDIA Corporation
OpenGL renderer string: NVIDIA GeForce RTX 4090/PCIe/SSE2
OpenGL core profile version string: 4.6.0 NVIDIA 595.58.03
OpenGL core profile shading language version string: 4.60 NVIDIA
OpenGL version string: 4.6.0 NVIDIA 595.58.03
OpenGL ES profile version string: OpenGL ES 3.2 NVIDIA 595.58.03

Session type:

wayland

Installed relevant packages:

local/webkit2gtk-4.1 2.50.6-1
local/egl-gbm 1.1.3-1.1
local/egl-wayland 4:1.1.21-1.1
local/egl-wayland2 1.0.1-1.1
local/egl-x11 1.0.5-1.1
local/lib32-nvidia-utils 595.58.03-1
local/linux-cachyos-lts-nvidia-open 6.18.20-1
local/linux-cachyos-nvidia-open 6.19.10-1
local/linux-firmware-nvidia 1:20260309-1
local/nvidia-utils 595.58.03-1

What I tested

I tried the following without meaningful improvement:

portmaster
WEBKIT_FORCE_COMPOSITING_MODE=1 portmaster
WEBKIT_DISABLE_DMABUF_RENDERER=1 portmaster
GSK_RENDERER=gl portmaster

I also tried:

GDK_BACKEND=x11 portmaster

This produced a slight UI difference, but Portmaster still felt sluggish/laggy.

Behavior observed:
Portmaster starts successfully
UI opens successfully
Backend/API connection seems normal
Issue is specifically about sluggish/janky UI responsiveness
X11 path behaves a bit differently than Wayland, but not enough to solve it

Logs

Startup logs look mostly normal and are very similar between the different launch methods. Repeated messages include:

[arboard::platform::linux][WARN] Tried to initialize the wayland data control protocol clipboard, but failed. Falling back to the X11 clipboard protocol.
[portmaster::config][ERROR] failed to load config file returning default config
Gtk-Message: Failed to load module "appmenu-gtk-module"
[portmaster::window][DEBUG] [tauri] main window page loaded: http://127.0.0.1:817/ui/modules/portmaster/

The app still loads and connects:

[portmaster::portmaster::websocket][INFO] Successfully connected to portmaster
[portmaster][INFO] connection established, creating main window

Is this a known WebKitGTK / Wayland / NVIDIA issue on Linux, and is there any recommended workaround or debug flag I should try beyond the env vars above?

I should also note that I tested it on windows as well (dual boot, same machine) and it was perfectly smooth with no UI issues.

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