How to activate stereo mix in Windows 10

Hi Guys. I have installed in my PC Windows 10 64 bit and recently downloaded Audacity 3.1.0. The problem: I don’t find how to activate stereo mix for this Audacity version in Windows 10. Can somebody help me?

Stereo Mix is becoming rare… [u]WASAPI (loopback)[/u] is similar.

You may have StereoMix, it could be disabled/hidden by default.
Has to be enabled before Audacity can “see” it …