Here is Baldy Catz explaining refraction. He is a number one educator in my book and has some very good content for educational purposes. This is another subject matter that I have seen Flat Earth individuals get terribly wrong. I have personally heard people like Sleeping Warrior get this completely wrong in debates just to be corrected by someone like Craig from FTFE.
Refraction By Baldy Catz
I will admit, it is one of the more difficult subjects for people but just because something is hard to understand does not mean that it is not true. Hence why physicists spend so much time in school and then in the field afterwords. All people like Sleeping Warrior is act like a child and “relieve themselves” all over scientific discoveries and the scientists behind them, which really makes them out to be simply a terrible human being.