Since upgrading to Debian trixie (which now runs KDE/Plasma6 based on Qt6) most Kde6 apps don't open anymore when using the proprietary nvidia driver (340.*)

BTW, there is no issue with KDE5 and the proprietary driver (eg. on Debian bookworm). Gnome desktop and Gnome applications, as well as the latest firefox-esr also work fine on trixie with the proprietary nvidia driver.

Programs crash like this:

qt.qpa.gl: Choosing xcb gl-integration based on following priority
 QList("xcb_glx", "xcb_egl")
qt.qpa.gl: Xcb GLX gl-integration created
qt.qpa.gl: Xcb GLX gl-integration successfully initialized
qt.qpa.gl: Requested format before FBConfig/Visual selection: QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize -1, redBufferSize 8, greenBufferSize 8, blueBufferSize 8, alphaBufferSize -1, stencilBufferSize -1, samples 4, swapBehavior QSurfaceFormat::DefaultSwapBehavior, swapInterval 1, colorSpace QColorSpace(), profile  QSurfaceFormat::NoProfile)
qt.glx: qglx_findConfig: Failed to finding matching FBConfig for QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize -1, redBufferSize 1, greenBufferSize 1, blueBufferSize 1, alphaBufferSize -1, stencilBufferSize -1, samples 1, swapBehavior QSurfaceFormat::SingleBuffer, swapInterval 1, colorSpace QColorSpace(), profile  QSurfaceFormat::NoProfile)
qt.qpa.gl: No XVisualInfo for format QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize -1, redBufferSize 1, greenBufferSize 1, blueBufferSize 1, alphaBufferSize -1, stencilBufferSize -1, samples 1, swapBehavior QSurfaceFormat::SingleBuffer, swapInterval 1, colorSpace QColorSpace(), profile  QSurfaceFormat::NoProfile)
qt.glx: qglx_findConfig: Failed to finding matching FBConfig for QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize -1, redBufferSize 1, greenBufferSize 1, blueBufferSize 1, alphaBufferSize -1, stencilBufferSize -1, samples 1, swapBehavior QSurfaceFormat::SingleBuffer, swapInterval 1, colorSpace QColorSpace(), profile  QSurfaceFormat::NoProfile)
qt.glx: qglx_findConfig: Failed to finding matching FBConfig for QSurfaceFormat(version 2.0, options QFlags<QSurfaceFormat::FormatOption>(), depthBufferSize -1, redBufferSize 1, greenBufferSize 1, blueBufferSize 1, alphaBufferSize -1, stencilBufferSize -1, samples 1, swapBehavior QSurfaceFormat::SingleBuffer, swapInterval 1, colorSpace QColorSpace(), profile  QSurfaceFormat::NoProfile)
Could not initialize GLX

A few examples of such KDE programs are: sddm, kwin, plasmashell.

I found that the OpenGL examples shipped in Qt6 are actually also crashing the same way. So this looks more like a problem with Qt6.

For instance these qtbase examples are all failing when using the "nvidia-legacy-340xx" driver (Nvidia proprietary driver v340.*). It happens on both linux kernel 6.1 & 6.12, so this is probably not related to the kernel itself.

• examples/opengl/2dpainting
• examples/opengl/cube
• examples/opengl/hellogl2
• examples/opengl/hellogles3
• examples/opengl/openglwindow
• examples/opengl/stereoqopenglwidget
• examples/opengl/textures

Workaround is to use the "nouveau" driver, but it is buggy in other aspects (random system crashes/freezes) which make this solution not appropriate.

You can find in attachment:

• output of various glxinfo calls for each driver.
• output of the examples for each driver when invoked with
  QT_LOGGING_RULES="qt.qpa.gl=true" /usr/lib/x86_64-linux-gnu/qt6/examples/opengl/2dpainting/bin/2dpainting  > 2dpainting.out 2>&1
  QT_LOGGING_RULES="*=true" /usr/lib/x86_64-linux-gnu/qt6/examples/opengl/2dpainting/bin/2dpainting  > 2dpainting.out.full 2>&1

Files ending with .out are produced with QT_LOGGING_RULES="qt.qpa.gl=true"
Files ending with .out.full are produced with QT_LOGGING_RULES="*=true"

Expected behaviour:

That the examples and kde6 programs open and display successfully with the nvidia driver (like it does with the nouveau driver with Qt6/KDE6 or nvidia driver with Qt5/KDE5)