No input signal with correct audio channels/hardware settings

CC 2018. The subject pretty much says it all. I've been messing with this for over an hour and I cannot get input from Windows10 running Chrome or from Premiere playing in the background over the stereo mix. I've watched the set-up videos and everything looks correct. I have updated the drivers (already latest drivers installed for Realtek audio, which is the recording channel). There is simply no input signal and nothing records, even though I can hear everything fin through headphones.

When I switch recording devices I get a strange anomaly: for a split second the meter registers whatever is playing in the background, but then it freezes (same for both Dynamic and Static peak settings), and it still will not record. When I try to record and scrub through, it plays a low hum, although there is no waveform.