virt-manager doesn't show list of local KVMs but virsh does

Check the output of virsh uri. It it returns qemu:///session, but you're using a qemu:///system connection in Virt-Manager, you found the cause.

In order to fix it, you should either create a "QEMU/KVM user session" connection in virt-manager, or run virsh define ~/.config/libvirt/qemu/<filename>.xml as root. This will create the xml definition under /etc/libvirt/qemu which will then be picked up by virt-manager.

If you see a connection for localhost (QEMU) listed, double click it.

If you don't see any connections listed, go to File > Add Connection, leave all the defaults set as they are, then click Add.