Hi @ralfb1, try the steps below:
Please open Device Manager > Find Parallels Audio Controller > Uninstall > right-click on Computer (at the top of the list) > Scan for hardware changes
Reboot the virtual machine and check how it goes.
Hi @costabas, may be the Windows updates have caused this issue. If you have a Time Machine backup, please try to restore the virtual machine. Refer to this article.
Hi Jefferis, since Windows 7 and Windows 10 are two different virtual machines you cannot use the same application installed in one virtual machine to the other. We do not have the option to import the application however, you can install all the required applications.