And virt-manager indeed manages Libvirt machines so it's not at the level of QEMU as you wrote in the parent comment:
> Proxmox is a virtual machine manager (like QEMU, virt-manager)
Straight from their site. QEMU is the user space interface, KVM the kernel space driver. It’s enough to run whatever OS. That’s the point.
For libvirt: https://libvirt.org/drivers.html
They support a bunch as well.