KDE does not work after Fedora 34 → 36 upgrade

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After I upgraded my system from Fedora 34 to 36 I can’t start X with KDE. Xfce works fine. If I use KDE I run “startx”, the screen goes black for a split second, then X exits. Nothing remarkable appears in the X log. I see it adding various devices, then removing various devices. How do I diagnose this?

I have an AMD GPU.