How should I deal with my brother, from whom I discovered pornographic materials on his device, knowing that he is considered religiously committed? What is my responsibility towards him? Should I inform my family or conceal his matter? And should I cut off the internet or monitor him?

You must conceal your brother's faults and not expose him before people, for the Messenger of Allah, peace and blessings be upon him, said: "If you follow people's faults, you will corrupt them, or you will be close to corrupting them," and he also said: "Whoever conceals a Muslim, Allah will conceal him on the Day of Resurrection." However, this concealment does not mean refraining from denouncing him, advising him, and admonishing him in private, especially if the brother is among the righteous, for Islamic law is more keen on concealing the faults of such individuals. Also, it is not permissible to inspect his device, as this is a blameworthy form of spying. Allah the Almighty said: "O you who have believed, avoid much [negative] assumption. Indeed, some assumption is sin. And do not spy." This may also lead to the person inspecting falling into temptation themselves. As for cutting off the internet at home, it is possible if it will reduce the chances of falling into such temptations. And you must continue to advise your brother and remind him, for he is afflicted and needs help.