Yeah the error message has nothing to do with your sound issue.
To allow your inputs and outputs to be used by multiple applications :
In Cubase, the selected audio device is automatically used at the project sample rate.
Open the Studio Setup and uncheck Release Driver when Application is in Background.
Hovever, in the case you are using the Generic Low Latency ASIO Driver, this box should be kept checked, because this particular driver is not multi-client. More information about this here that you need to understand.
Open the sound settings in Windows.
To go there directly, press Win+R and paste control mmsys.cpl sounds
Now for every channel used by Cubase (or even better, do this for all), double click to open the properties dialog, and under Advanced tab, change the default sample rate to match Cubase sample rate and bit depth, and uncheck Exclusive Mode (Allow application to take exclusive control of this device).
You can eventually right-click on channels that you don’t want to use and disable them, notably Realtek devices, Optical, and HDMI Audio. That way, only the channels that you use will be displayed in programs and drivers, that’s cleaner.
Subsequently, make sure that any program are also set to this same sample-rate, for example video editors etc. This must be coherent system-wide.