Give real effort in the class you think is easy. Coasting is a habit, and habits don’t stay in one room.

Coasting is not a decision about one subject, it is a setting that spreads. Once you learn that seventy percent of your attention buys an acceptable result, seventy percent becomes the amount you bring by default, including to things you care about. The easy class is where that habit gets rehearsed quietly, with no cost to warn you.

Take the class you currently sleepwalk through and do one assignment fully. Not for the grade, which will barely move. Do it to find out what your actual full effort feels like, since you may have lost track.