Parallels Desktop cannot be started or installed on macOS Big Sur Beta 3.

export SYSTEM_VERSION_COMPAT=1

open -a "Parallels Desktop"

If Parallels Desktop is already installed, temporary workaround is to run Parallels Desktop as shown below:

1. Open Terminal (Finder > Applications > Utilities > Terminal).
2. Execute the following commands one by one:
   export SYSTEM_VERSION_COMPAT=1 open -a "Parallels Desktop"

If Parallels Desktop fails to install, do the following:

1. If Parallels Desktop App Store Edition is installed, uninstall it.

2. Download Parallels Desktop 15 installation file. Other Parallels Desktop versions can be downloaded here

3. Double-click the downloaded file to mount it.

4. Open Terminal (Finder > Applications > Utilities > Terminal) and execute the following commands one by one:

   sudo -E -s
   (You will need to enter your Mac password to run the command. No symbols will be shown due to security measures, so just hit the keys and use Return/Enter.)

   cd /Volumes/Parallels\ Desktop\ 15
export SYSTEM_VERSION_COMPAT=1
open Install.app

5. If the installation is successful, run Parallels Desktop by following the instructions above