Latest version of Audacity 3.2.1 Hi I select Stereo Mix in audio setup / input device it appears it is enabled in windows, but it does not record. I have SOUND TAP a utility for recording anything playing on my computer it has no problem. This used to work in Win 7 but not Win 10 what is wrong here.
Stero Mix recording works for me on Windows 10 with Audacity 3.2.1 using Host MME, Direct Sound, and WASAPI. You might check that the volume is turned up.
Note that for loopback recording many people are using WASAPI and “Speakers (loopback)” as their recording device. Also, Transport > Rescan Audio Devices might fix your issue.