Unable to disable SIP on BigSur
Last time I updated my Mac from macOS Catalina (10.15.5) to Big Sur  Beta 1, SIP was enabled again.
But I can't ensure you that it will work.
I found this on Google :

'Power on to firmware' from the Virtual Machine menu

Select 'Enter Setup'

Boot from the file

Arrow down to Recovery HD

Hit Enteruntil you can pick boot.efi

Select boot.efi

Hit Enter and you should now be able to disable SIP.