Are the invocations mentioned in the question considered among the post-prayer remembrances? What is the evidence for repeating Ayatul-Kursi and Surahs Al-Ikhlas and Al-Mu'awwidhatayn three times after the Fajr and Maghrib prayers? When should the supplication "Allahumma ighfir li dhunubi wa khatayaya kullaha..." (O Allah, forgive all my sins and mistakes...) be recited? Is the remembrance mentioned in Jabir's hadith regarding reciting "Qul Huwa Allahu Ahad" ten times after every obligatory prayer authentic?

The first remembrance: "O Allah, forgive all my mistakes and sins..." reported by Al-Tabarani with a good chain of transmission, and it is among the remembrances recited after prayer.

Reciting Ayah al-Kursiy, the Mu'awwidhat (Surahs Al-Falaq and An-Nas), and Qul Huwa Allahu Ahad (Surah (definition) Al-Ikhlas (definition)) are among the remembrances recited after prayer. However, there is no specific evidence for reciting them three times specifically after Fajr and Maghrib prayers; rather, this is part of the morning and evening remembrances.

Reciting Al-Fatihah is not among the remembrances recited after prayer.

Seeking forgiveness three times is among the remembrances recited after prayer, but without adding "Al-Azim wa atubu ilayh" (the Great and I repent to Him).

The supplication "O Allah, make the best of my life its end..." is very weak.

The supplication "O Allah, our Lord and the Lord of everything" is weak and not among the remembrances recited after prayer.

Jaber's hadith (definition) mentioned by the questioner is very weak.