You'll need to build a new kernel. The one in WSL2/Ubuntu isn't compiled with KVM support. Once you do that, it should work fine.

I've attempted several times today but haven't successfully gotten KVM working with the custom kernel. Thanks for pointing me in this path.

AMD KVM in WSL and basically anything that relies on the Windows Hypervisor won't work yet on AMD CPUs. You have to disable the Hypervisor support in Windows which allows other KVM capable VM managers like Qemu, Virtualbox, and VMWare to all run KVM VMs on AMD on Windows. Look at the 3rd or 4th answer here if you want two boot entries to be able to enable or disable the Windows Hypervisor at boot time from the boot menu. https://superuser.com/questions/540055/convenient-way-to-ena...