If you want to run Windows VMs with all the security features enabled, xcp-ng / xen is a non-starter as it's been completely broken for years with no fix in sight:
Proxmox / KVM is the only alternative to ESXi that can support all of Windows security mitigations such as Core Isolation, which requires nested virtualization.
I would not switch an enterprise from VMWare -> Proxmox without a really thorough analysis of what that will mean.
That said the future of VMware is certainly in question.