Antonyms for "became adept in" include "struggled with," "failed at," "inept," "amateur," and "novice." These words describe a lack of skill or proficiency in a particular area or activity. To be inept or a novice is to lack experience or knowledge, while struggling with or failing at something suggests a difficulty or inability to grasp the concepts needed to perform the task at hand. It's important to remember that everyone has strengths and weaknesses, and it's okay to be less than "adept" in certain areas. With time and practice, anyone can improve and become more proficient in their skills.