Broadly speaking, you're going to run #Linux on your #mainframe on z/VM or #KVM (living on a tiny Linux install itself on the LPAR).
z/VM has tons of knobs and is incredibly rich with features going back decades, but KVM integrates seamlessly into all the other stuff you may be using that supports KVM (all hail libvirt!). So it's always nice to read through the quarterly updates to KVM that help improve that experience http://kvmonz.blogspot.com/2023/07/kvm-in-linux-distributions-in-2q-2023.html
@pleia2 kvm/libvirt is the gold standard in my opinion! If it were to ever go away on any architecture I don’t think that architecture would ever recover.