فَقَدَّرَ ذَلِكَ تَقْدِيرًا مُحْكَمًا مُبْرَمًا
Allah has determined it through a firm and definitive decree.
Muḥkam indicates firmness and certainty; mubram signifies a conclusive decree not subject to alteration by creatures. Allah determines matters according to His knowledge, and no one else can add to, subtract from, or modify this definitive judgment.