I have a macOS 10.15.5 VM I created using Parallels on macOS. I don't want to upgrade my main OS to the Big Sur beta just yet, so I was hoping to run in in a VM to see how things are before trusting it on my main OS installation. I've gone through the documented steps to enable the Apple Beta Software Program on the VM, but for some reason it will not detect the Big Sur update as being available for install. It's like Apple is blocking the Big Sur beta from being installed on a VM... Does anybody know if this is true? Or, do you have any tips on how to get macOS Big Sur beta installed on a macOS VM running in Parallels Desktop?
See https://github.com/rtrouton/create_macos_vm_install_dmg for a way to create a Big Sur installer disk image. For this to work, you need to download the Installer app onto your main Mac, run the script to create the disk image and then run Parallels with that image to create a Big Sur VM.
Performance may be rather unsatisfactory though, you might be better off with installing Big Sur on an external drive or separate partition, and boot from there.