In this context, ‘This’ is the adjective, as it describes the amount of Karens there are in this sentence. Karen is indeed the noun in this situation.
An example of using ‘Karen’ as an adjective would be: ‘did you how so-and-so went completely Karen on that clerk?’
You visualize how so-and-so acted in a particular way towards the clerk. The adjective to describe the behavior was ‘Karen’.
Hope that clears things up.
It didn’t though. Christmas was invented by the Christians to help convert Pagans of the time by saying that Christianity fits in with their celebrations. Christmas origins come from the Roman celebration of Saturnalia.