Note that if you not only don't have the stereo mix / waveout mix, but also have the No audio output problem, you need to download and install the latest version of the driver or update it. You can also try the following:

• In the Device Manager right click and disable your audio. Then right click and enable it.
• Plug in external stereo speakers to the stereo jack. Windows detects whether anything is plugged into the stereo jack. After recognizing the speakers, it should install the driver.
• Re-install the driver in the Safe mode.

More solutions:
Problem: Missing sound recording option: No Stereo Mix, Wave-out Mix, Record What You Hear option