When it comes to antonyms for "becomes adept in," there are a few options to consider. One could use inexperienced or unfamiliar to describe someone who has not yet become skilled in a particular area. Another option might be the word incompetent, which suggests a lack of ability or knowledge. Another antonym could be amateurish or unskilled, indicating a lack of professional ability or expertise. It's important to keep in mind that antonyms can vary in meaning depending on context, so it's always best to choose the word that best fits the situation at hand.