I think even if this El Clasico was not in the Copa Del Rey and it was in La Liga where Real Madrid had no hopes for it, they still had to focus on this team much more than other games because Barcelona won three matches against Real Madrid and if they lose another game, it can put Real Madrid under pressure, however, they are so ready for the match after the game they won before El Clasico.
All matches between Barcelona vs Real Madrid are El clasico matches. Be it in the Copa Del Rey or the League, even all the games if they meet. The difference is just that the match in the League feels difficult to restore Madrid's chances of winning even though it wins because of the already large difference in points. While the best opportunity I think is in the Copa Del Rey. Madrid still has a chance to qualify for the final.