Did you also do the

“bcdedit /set hypervisorlaunchtype off” step in the KB?

That step seems to be quite common to be missed out.

You can also check if the Memory integrity is off. If it is "on", the ULM will also be used.

Windows Security -> Device Security -> Core Isolation details

Apart from these things, it is hard to say. Couple of weeks back, another poster with a Lenovo Thinkpad just did a clean install of Windows 11. After the KB followed, Memory integrity off, no antivirus (some antivirus use virtualisation features as well) and it still was using ULM and eventually he did a clean install of Windows 11 on the Thinkpad.

It might be Lenovo enabled other stuff.

You can download Windows 11 to USB using the Windows 11 Media Creator and do a clean/fresh install. At least this way you have some control of the Windows 11 host image.