I've got two Macs. On one of them, VMWare Fusion works great - I had v10, 11, 11.5, and now 12.
On my other Mac, I haven't been able to power on a VM since... Fusion 11? I just get "Failed to power on (path)" on ANY VM when I hit the start/play button.
I upgraded to Big Sur and installed VMWare Player 12 (I own VMWare 11.x, trying Player before I pay for the upgrade to the full version of 12) and am experiencing the same issues.
I've tried the following:
Uninstalled, including removing all Library files & even kexts, reinstalling.
"Allowed" the kernel extension
Disabling SIP in combination with the above.
Making sure VMWare has all permissions in the Privacy tab of System Preferences. Removing and re-adding it to all permissions.
Trying new VMs.
Making sure all other hypervisors are completely removed (namely Docker).
Must be some conflict with something that was installed on this mac at one time! I've been unable to find any relevant log files to give me more information. I think I've tried everything found in other search results here in this forum!