If that does not work it explains how to record streaming audio with Audacity ( which is free).
And then you could export the audio file into Mixcraft.
FWIW: I can't add Stereo Mix to my Windows 10 Lenovo laptop... So the above is what I have to do.
- Joe -
MX 8.1 Pro, Build 418, 64-bit. i5, 1.80GHz, 8GB, Windows 10. Focusrite Scarlett 2i4, Event and PreSonus monitors, Sony MDR-7506, Korg TR61, Akai MPK249, Fender P & J basses, Ric, Strat, D35, stomp boxes and a lot of microphones, etc.