Sorry for not looking a little harder. I think the answer is in @angry.sardine’s comprehensive whitelist “how-to” guide.
I’m still tinkering, but the solution that seems to work is to go to Settings>Player>Videos and set “Display 4:3 Videos As” to “Stretch 16:9”.
I’m tinkering with the “Minimize Black Bars” setting, but that doesn’t appear to be doing anything for me. But at least the resolution seems correct now.