I upgraded VMWare Fusion to version 12 in Big Sur lately. But the vmware-vmx process for the Windows guest system will take 150+ %CPU. Googling a bit that updating vmware tools seems not the solution, this forum thread and the origin source thread looks promising but actually doesn’t help.

After a few trials, disable Hypervisor in the Processor-Advanced will greatly lower the CPU, but some usb devices might also stop working. Finally, disable side-channel mitigation in the advanced settings helps quite a bit.

After shutting down the guest, and modifying the settings, the vmware-vmx process goes back to around 60-80% CPU.