Assuming this is in the bathroom, it is most likely the independent light switch for the bathroom? Interesting that your holding tank switch & tank meters are located there. My 19.3 has them located right of the cabinet above the dinette.
I'm sure that is the light switch for the bathroom. Looks like mine with no label.
Lol it was thanks the light wouldn’t turn on and I was like all confused..but the lights also switch by pressing the light itself in and it was in off position which why the main switch wouldn’t do anything.