On my laptop with Intel UHD Graphics 630 and modesetting driver I cannot start the compositor with OpenGL backend under X11. Up to Plasma 5.22 I used the XRender backend to fix the issue but it has been removed in Plasma 5.23. The kwin log in verbose mode just says:

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kwin_core: Available scene plugin: "/usr/lib/qt/plugins/org.kde.kwin.scenes/KWinSceneOpenGL.so"
kwin_core: Available scene plugin: "/usr/lib/qt/plugins/org.kde.kwin.scenes/KWinSceneQPainter.so"
kwin_core: Attempting to load the OpenGL scene
kwin_scene_opengl: Initializing OpenGL compositing
kwin_platform_x11_standalone: Global share context format: QSurfaceFormat(version 3.0, options QFlags<QSurfaceFormat::FormatOption>(DeprecatedFunctions|ResetNotification), depthBufferSize 0, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize 0, stencilBufferSize 0, samples -1, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 0, colorSpace QSurfaceFormat::DefaultColorSpace, profile  QSurfaceFormat::NoProfile)
kwin_core: Starting without compositing...
kwin_core: Failed to initialize compositing, compositing disabled


and I can't extract anything useful from this. Other OpenGL applications work fine so I'd say that the drivers are correctly installed. I tried to use both the Iris and the i965 Mesa drivers wthout success. All my attempts up to now are summarized here.

I'm clueless and a bit frustrated, so any help is greatly appreciated. Thanks.

I have enabled also the info, warning and critical log levels, and a new line has appeared in the log:

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kwin_scene_opengl: Creating the OpenGL rendering failed:  "Invalid QOpenGLContext::globalShareContext()"


This seems to be more useful, but still I can't make use of it.

I found that in ~/.config/kwinrc the GLPlatformInterface variable in the [Compositing] section was set to egl. I set it to glx and the compositor started working again.