

This file can simply be edited to set this value to true.

There is a VMX config parameter, monitor.allowLegac圜PU, which can be set either directly within the VM’s VMX file, or as a system-wide default in VMware’s config file at /Library/Preferences/VMware Fusion/config. Luckily, this has been discussed already on VMware Fusion forums and the solution was quick at hand. I learned only of the system’s incompatibility to show me the above notification after I was attempted to start an existing macOS VM from my VM library.

Originally I discovered this issue the hard way when VMware Fusion 8.5 on my MacPro4,1 system (dual 6-core X5550 CPUs) advertised the 10.0 upgrade, and happily let me run the upgrade on this system without any mention of this CPU feature requirement. Earlier versions had a more ambiguous dialog wording which didn’t explain the incompatible features, however it seems as though currently they seem to be providing more detailed info, mentioning the “unrestricted guest” capability.
