Scrap everything you know from the shows.
Take the most powerful version of Superman in the comics or shows. Take the most powerful version of Supergirl in the comics or shows and tell me who would win using actual explanations and canonical sources. Excuses like she’s a girl and he’s a man are not valid, but anything that is objective can be used. Excuses like oh she won on Supergirl is not valid because the source material is obviously biased considering it’s her show… things that showcase objectively her strengths compared to his are completely acceptable arguments.
You can even mix sources if you want. But who do you think would actually win in a fight with both heroes going full force with the most powerful versions of themselves.