Should I fold my legs after Fajr and Maghrib prayers and perform the specific dhikr, or should I remain in the افتراش (iftirash) sitting position? And if folding the legs is obligatory, what should I do in case of discomfort? And should I start the dhikr immediately, or after seeking forgiveness and saying "Allahumma Antas-Salam"?

It is prescribed to say, after the Fajr and Maghrib prayers, while in the Tashahhud (definition) posture: "None has the right to be worshipped but Allah alone, without any partner. To Him belongs all sovereignty and all praise. He gives life and causes death, and He is over all things competent." It is stated in Mir’at al-Mafatih Sharh Mishkat al-Masabih: "Before he departs, meaning from the place of prayer, and before he changes the posture of his legs—meaning before he bends and alters them from the Tashahhud position—after the Maghrib and Fajr prayers." And in the Hadith (definition) narrated by Abd al-Rahman ibn Ghanam from Abu Dharr, found in At-Tirmidhi: "Whoever says after the Fajr prayer, while still in the posture of his legs, before speaking—Al-Jazari said: meaning while his legs are bent in Tashahhud before he stands up." It is preferable to begin by seeking forgiveness three times after concluding the obligatory prayer.