Hi
@JohanF,
As macOS High Sierra is not officially released it is not supported by us. You can try disabling System Integrity Protection and check if you can use Parallels Desktop.
Follow these steps to disable SIP:
* Restart your Mac.
* Before OS X starts up, hold down Command-R and keep it held down until you see an Apple icon and a progress bar. Release. This boots you into Recovery.
* From the Utilities menu, select Terminal.
* At the prompt type exactly the following and then press Return: csrutil disable
* Terminal should display a message that SIP was disabled.
* From the menu, select Restart.
* You can re-enable SIP by following the above steps, but using csrutil enable instead.
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