Since Artix Linux updated to Qt 6.9.0, I experience KMail crashing shortly after starting up when using X11. This does not happen when using Wayland, and it also did not happen before the upgrade from QtWebEngine 6.8.3 to 6.9.0.

This does not happen on all of my machines. I suppose it's due to some hardware combination. After trying another graphics card, the crash didn't happen anymore.

I first wrote a report of the problem in the Artic forums: https://forum.artixlinux.org/index.php/topic,8014.0.html

Later on, I found a KDE bug report apparently describing my very issue: https://bugs.kde.org/show_bug.cgi?id=502578

In the KDE bug, it was claimed that setting 
QTWEBENGINE_CHROMIUM_FLAGS="--disable-gpu"
was a workaround. This indeed stopped KMail from crashing on X11 here.

I suppose this to be an upstream QtWebEngine bug – I'll happily help to track this down if I can. Would be nice if this could be fixed.