It’s come to our attention that some changes made for KWin in Plasma 6 aren’t compatible with the old and outdated software-rendering graphics drivers in VirtualBox. Thankfully there’s a solution: enable 3D acceleration in the machine settings. It not only resolves the issue, but also enables all the fancy graphical effects you would expect to see on a bare-metal installation. This is especially important if you’re using a VM for a review, screenshots, or videos of Plasma 6!
I’ve reached out to the VirtualBox devs regarding the possibility of making this happen automatically. But in case that doesn’t happen, it’s up to VirtualBox users to manually enable 3D acceleration in their machine settings.
Adventures in Linux and KDE 
For me, the latest VirtualBox 7.0.14 still crashes in its kernel module. But both virt-manager and gnome-boxes work (both using QEMU).
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You’re welcome to use whatever VM solution you want. This advice is simply for those who do use VirtualBox, since I know it’s a fairly popular piece of VM software.
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Yes, I do use VirtualBox. Was just providing a sample where the solution provided doesn’t solve the issue.
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Advice from an Ubuntu developer:
“Switch to VBoxSVGA graphics and disable 3d accel, it should work. The VMSVGA graphics drivers in Linux are missing a vital feature when 3d accel is off, but the VBoxSVGA driver has the needed feature even without 3d”
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