I believe that "solar plug" near your water bay is nothing more than a plug and two wires to connect to the battery. They provide a means to plug in a portable solar charging system, similar to the 100 watt "solar system) available at Harbor Freight. There is no wiring for roof mounted solar panels, no inverter loop, no inverter ready interior AC plugs and no "solar components" such as a charge controller or a battery shunt/monitor"...
All that type "solar ready plug" does is give you a means to plug in that portable system to charge your battery bank (if you have the red and black wires connected to the battery).....
In 2020 Cougars, the factory did install a "basic solar package" called the Off The Grid (OTG) system. I'm posted a part of the brochure that explains the "standard package which was installed in all trailers and the optional package that was only installed in trailers special ordered with the extra cost option"...
Then, in 2021, Keystone started installing the SolarFlex systems. The SolarFlex 200 is the "standard package" and does not include an inverter, but there is an "inverter loop" that provides a means to install an inverter to power specific outlets in the trailer (usually 3 to 5 total outlets).
The extra cost optional SolarFlex 400i is the first available "solar package with an inverter" installed by the factory in the Cougar line.....
You can download the 2018 and newer Cougar brochures on the Keystone website:
https://www.keystonerv.com/brochures#archive The brochures will show you the "evolution from your "plug and wires to the battery" to the present day SolarFlex systems....