Is it just for God to create the disbeliever or the wicked, knowing in advance that they will be among the wretched in the Hereafter, or is their creation in this world merely to establish a case against them in the Fire, especially considering that the majority of creation will be among the people of the Fire?

One must avoid delving into the topic of divine decree (Qadar (definition)), as it leads to perdition. Furthermore, delving into such questions raises doubts and suspicions. A Muslim must believe that Allah is All-Knowing, All-Wise, All-Just, All-Merciful, and that He wrongs no one, and He is not questioned about what He does. The existence of a disbeliever, despite Allah's knowledge of their ultimate destiny, does not contradict His justice, because He holds creation accountable for their actions and their choice of disbelief or faith. Allah has granted His servant choice, will, and volition.