Do you know if there is any plan to address: "The issue of the nested virtualisation only affects Workstation Pro 15.5.5 and later running on Windows 10/11 host OS with Hyper-V enabled."
Short Answer:
I don't know. I don't work for VMware and even if I do, I should not be saying anything. But I guess it is likely a limitation of the Microsoft Windows Hypervisor API. So I don't think you should be waiting for a fix to come anytime soon. The problem has been around for 4 years now, longer if you count back to 2017.
Long Answer (with a little bit of history):
The nested virtualisation capability (aka VT-x capability inside VMware VMs) has been around since 2011 (Workstation 8.x on Windows/Linux, Fusion 4.x on macOS and ESXi 5.x).
When Windows 10 1709 was released (the first version that had WSL), Workstation 12.5.x would basically crash when the Windows 10 1709 had WSL installed due to the conflict with Hyper-V. So Workstation 12.5.x, 14.x, 15.0.x users on Windows hosts had to disable WSL/WSL2, Hyper-V, Device Guard, among other things.
When Workstation 15.5.5 was released, Workstation could now co-exist with Hyper-V enabled on a Windows 10 host. The approach was to use Windows Hypervisor API which would run on userspace (presumably ULM means Userspace Level Monitor) instead of making Intel VT-x calls directly at the kernel level (CPL0 means current privilege level 0, which is Intel terminology for running at ring 0/kernel level).
https://blogs.vmware.com/workstation/2020/05/vmware-workstation-now-supports-hyper-v-mode.html
Aside from the performance downside with ULM, nested virtualisation will not work, neither will virtualised performance counters (VPMC). But with CPL0, nested virtualisation works the same way it does since version 8.x plus with all the improvements in Intel VT-x in newer generations of CPUs.
So this problem of "nested virtualisation" does not affect Linux hosts and ESXi hosts at all.
For Fusion on macOS, starting with Big Sur, Apple disallowed the use of macOS kernel extensions and Fusion 12.x had to use the Apple Hypervisor Framework API. On Fusion, the nested virtualisation on Intel Macs was not available for a few months and VMware added nested virtualisation on a minor update.
If you compare the Microsoft Hypervisor API and Apple Hypervisor API online documentation, the Microsoft docs looks quite bare;
https://learn.microsoft.com/en-us/virtualization/api/hypervisor-platform/hypervisor-platform
while the Apple docs you can even see that there is a reference to VMCS Shadowing (which is used in Intel CPUs for better nested VM performance).
https://developer.apple.com/documentation/hypervisor/3182868-hv_vmx_vcpu_set_shadow_access?language=objc
Fusion on Apple Mx chips still don't have nested virtualisation though.