Setup:  <Host> macOS Big Sur Public Beta 1 Build 20A5343j <Guest> Win 10 Ult <Scenario-1> After macOS Big Sur upgrade, VM won't start. Used commands: export SYSTEMVERSIONCOMPAT=1; open -a 'Parallels Desktop'. VM was up and Win OS started working. Shutdown. Restarted VM with the same procedure. VM was up and Win OS started working. Re-installed Parallel Tools. System Crashed and could not make it work. <Scenario-2> Installed Parallels v15.1.4. Tried all the prescribed workaround steps. But none of them worked. <Workaround - Success> Went into Time Machine and replaced the Parallels v15.1.4 with the last working copy before upgrading to Big Sur. Used commands: export SYSTEMVERSIONCOMPAT=1; open -a 'Parallels Desktop'. SUCCESS. VM is up and OS working and peaceful shutdown. Restarted the VM and OS. SUCCESS. Was able to work.Note* Do NOT try to change the Config setting of Parallels, which will crash the VM and OS becomes unresponsive. Wish you all the best.