Bug 499322

SUMMARY
On X11, with KWIN_COMPOSE=N, it is impossible to run another compositor

STEPS TO REPRODUCE
1. Run KWIN_COMPOSE=N kwin_x11 --replace
2. run picom


OBSERVED RESULT

picom --diagnostics
**Version:** v12.5 (/startdir/picom revision a456d43)

### Extensions:

* Shape: Yes
* RandR: Yes
* Present: Present

### Misc:

* Use Overlay: No
  (Another compositor is already running)
* Config file specified: None
* Config file used: /etc/xdg/picom.conf

### Drivers (inaccurate):

modesetting

### Backend: glx

* Driver vendors:
 * GLX: Mesa Project and SGI
 * GL: Intel
* GL renderer: Mesa Intel(R) Iris(R) Xe Graphics (TGL GT2)
* Accelerated: 1
[ 30/01/2025 14:17:35.954 egl_init WARN ] The egl backend is still experimental, use with care.

### Backend: egl

* Driver vendors:
 * EGL: Mesa Project
 * EGL driver: iris
 * GL: Intel
* GL renderer: Mesa Intel(R) Iris(R) Xe Graphics (TGL GT2)


EXPECTED RESULT
Picom shuld not found another compositor running


SOFTWARE/OS VERSIONS
Operating System: Manjaro Linux 
KDE Plasma Version: 6.2.5
KDE Frameworks Version: 6.10.0
Qt Version: 6.8.1
Kernel Version: 6.13.0-1-MANJARO (64-bit)
Graphics Platform: X11
Processors: 8 × 11th Gen Intel® Core™ i5-1135G7 @ 2.40GHz
Memory: 15.4 GiB of RAM
Graphics Processor: Mesa Intel® Iris® Xe Graphics