I looked in my settings for Gmail and have the option for dark theme. I do not have any such option for the Play Store and it is still light.
You are correct! I read that and changed my device theme to dark and now the Play Store and some other apps are displaying dark.I might be wrong, but I believe that the Play Store theme is set automatically to match your device theme. So if you have system-wide dark mode enabled, the Play Store should go dark.