To what extent is what was stated in an article on the "Ahl al-Qur'an" website true, that what exits at the time of death is the nafs (self/psyche) and not the ruh (spirit/soul), and denying the existence of the two angels and the questioning and torment of the grave, and that a person after their death is like one sleeping until the Day of Judgment, with the author mentioning scientific proofs and proofs from the Qur'an?

The reality of death is the soul's departure from the body, and the nafs (self/psyche) is the ruh (spirit/soul). The torment of the grave and the trial of the grave (questioning by the two angels) are established by the Quran and Sunnah (definition). The claim that the deceased is like one sleeping: if the intent is the state of repose, then yes; but if the intent is the absence of trial, torment, or bliss, then it is a denial of the Quran and Sunnah. The website mentioned belongs to the zanadiqah (heretics/apostates) who deny the Sunnah.