Is the Samaritan who lived at the time of Moses the Antichrist (Al-Masih Ad-Dajjal), and why was he released after his deed while others were commanded to kill themselves?

The Samaritan is not the Dajjal. The prophets warned their nations about the Dajjal and his characteristics. If the Samaritan were the Dajjal, his matter would not have been hidden from Moses and Aaron, peace be upon them. Furthermore, Allah punished the Samaritan by decreeing that he should not touch anyone, as He said: "Go, then! Indeed, it is decreed for you in this life that you will say, 'No contact!'" (Surah Taha, 20:97). In contrast, the Dajjal will mix with people at the end of time. No one ever claimed that the Samaritan was the Dajjal before contemporary claims for which there is no evidence, and the Dajjal will emerge from the East.

The difference between the Samaritan and those from Moses's people who repented is that the Samaritan did not regret his actions and did not wish to repent; rather, he said: "I saw what they did not see" (Surah Taha, 20:96). As for the people, they regretted and sought Allah's forgiveness, and Allah accepted their repentance on the condition that some of them kill others.