Hello, my name is Marco and I am an Independent Advisor. I will do my best to help you.
Press Windows + R and type: mmsys.cpl
Go to the “Recording” tab
Right-click on a blank space and then check the option “Show Disabled Devices“
If you see ‘Stereo Mix‘, right click and check 'enable'.
Then, click apply and OK.
If you don't see it, your audio driver may not be up to date or your hardware may not support it.
Go to the manufacturer's website to download the latest chipset driver and check if 'stereo mix' is now available.