virt-manager: KVM is not available

Your journalctl output shows:

Oct 14 22:23:00 okcomputer libvirtd[35615]: Failed to probe capabilities for /usr/bin/qemu-system-x86_64: internal error: Failed to start QEMU binary /usr/bin/qemu-system-x86_64 for probing: /usr/bin/qemu-system-x86_64: symbol lookup error: /usr/lib/libvirglrenderer.so.1: undefined symbol: gbm_bo_unmap

Try just running /usr/bin/qemu-system-x86_64 -help and you'll likely see the same error. These undefined symbol errors happen when the version of qemu that is installed does not match the version of the referenced library that it was built against.

I don't know the specifics on Arch, but on Fedora the relevant package is called virglrenderer. It likely needs to be upgraded

The reason this manifests itself as KVM is not available is that libvirt (and by extension virt-manager) didn't find a working qemu version that matches your host architecture, which is necessary for KVM to work.

Your problem is: opencl-amdgpu-pro-orca.
It delivers its own libgbm.so.1 which is missing that symbol even with latest AUR version with a default. It is put in search path first.
So You can disable these drivers or try to get / compile a fixed / updated version that includes this feature - or try to disable that lib search path only for the libvirtd servcie (add LD_LIBRARY_PATH=/usr/lib environment variable to service startup procedure).

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How to analyze such issues for example:

ldd /usr/lib/libvirglrenderer.so.1
ldd /usr/lib/libvirglrenderer.so.1|awk '$3!=""{print $3}'|while read file; do objdump -TC -j.text $file|grep gbm_bo_unmap && echo $file; done
LD_LIBRARY_PATH=/usr/lib ldd /usr/lib/libvirglrenderer.so.1|awk '$3!=""{print $3}'|while read file; do objdump -TC -j.text $file|grep gbm_bo_unmap && echo $file; done