"acada mode" means the state of locking in and going full focus on studying — cutting off distractions, declining social invitations, and dedicating all energy to academic work. It is one of many casual words teens pick up from friends, social media, music or sport, and on its own it carries no particular warning. If you hear your teen use it, it is fair to ask what they mean by it in their friend group, since meanings drift quickly. Asking out of curiosity rather than alarm tends to keep the conversation open and useful.