Mac OS Catalina, uneven battery drain in AirPods
I noticed last night that my left pod drains faster than my right, and doing your test just now, I can see that (with Automatically Switch AirPods selected) my left pod microphone shows input volume but my right does not.

Update: I have found that my AirPods (2nd Gen) are evenly charged with left and right double-tap turned off, and sound input set to internal microphone. I suspect that selecting AirPods for input source was the main issue.