What is the Shar'i ruling on my falling short in my studies and feeling a lack of desire for them, despite my awareness of their importance, and what is incumbent upon me to do regarding that?

Your academic underperformance without a valid excuse is displeasing, and you are blameworthy for it. You must be sagacious, cautious, resolute, and take the necessary means. If you are overcome, then say: "Allah is sufficient for me, and [He is] the best Disposer of affairs."

The strong believer, in his resolve and determination, is better and more beloved to Allah. So, be eager for what benefits you, seek Allah's help, and do not become helpless. Do not say: "If only I had done such and such, it would have been such and such," but rather say: "Allah has decreed, and what He willed, He did."

The incapable person is one who follows his desires and wishes for mere hopes. The predecessors disliked wasting time.

Strive hard in your studies and excel, rely on Allah, and supplicate to Him to protect you from incapacity and laziness. Seeking beneficial knowledge is an act for which you are rewarded, as is bringing joy to your family through your excellence.